Added rule for dropdown accessibility

docs/rules/dropdown-needs-arialabeledby-and-label-v9.md

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+# Accessibility: Dropdown mising label or missing aria-labelledby (`@microsoft/fluentui-jsx-a11y/dropdown-needs-arialabeledby-and-label-v9`)
+
+<!-- end auto-generated rule header -->
+
+Accessibility: Dropdown menu must have a visual label and it needs to be linked via aria-labelledby
+
+<https://www.w3.org/WAI/WCAG22/Techniques/aria/ARIA16>
+
+## Ways to fix
+
+-   Add a label with an id, add the aria-labelledby having same value as id to dropdown.
+
+## Rule Details
+
+This rule aims to make dropdown accessible
+
+Examples of **incorrect** code for this rule:
+
+```jsx
+<Dropdown />
+<Dropdown aria-labelledby="dropdown-id"></Dropdown>
+```
+
+Examples of **correct** code for this rule:
+
+```jsx
+<>
+<Label id="dropdown-id" />
+<Dropdown aria-labelledby="dropdown-id"></Dropdown>
+</>
+```

lib/rules/dropdown-needs-arialabeledby-and-label-v9.js

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+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+"use strict";
+
+var elementType = require("jsx-ast-utils").elementType;
+const { hasAssociatedLabelViaAriaLabelledBy } = require("../util/labelUtils");
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        // possible error messages for the rule
+        messages: {
+            missingLabelOrAriaLabeledByInDropdown: "Accessibility: Dropdown mising label or missing aria-labelledby"
+        },
+        // "problem" means the rule is identifying code that either will cause an error or may cause a confusing behavior: https://eslint.org/docs/latest/developer-guide/working-with-rules
+        type: "problem",
+        // docs for the rule
+        docs: {
+            description: "Accessibility: Dropdown menu must have a visual label and it needs to be linked via aria-labelledby",
+            recommended: true,
+            url: null
+        },
+        schema: []
+    },
+
+    // create (function) returns an object with methods that ESLint calls to “visit” nodes while traversing the abstract syntax tree
+    create(context) {
+        return {
+            // visitor functions for different types of nodes
+            JSXOpeningElement(node) {
+                // if it is not a Checkbox, return
+                if (elementType(node) !== "Dropdown") {
+                    return;
+                }
+
+                // if the dropdown has a aria-LabeledBy with same valye  return
+                if (hasAssociatedLabelViaAriaLabelledBy(node, context)) {
+                    return;
+                }
+
+                // if it has no visual labelling, report error
+                context.report({
+                    node,
+                    messageId: `missingLabelOrAriaLabeledByInDropdown`
+                });
+            }
+        };
+    }
+};

tests/lib/rules/dropdown-needs-arialabeledby-and-label-v9.js

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+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const RuleTester = require("eslint").RuleTester;
+
+const rule = require("../../../lib/rules/dropdown-needs-arialabeledby-and-label-v9");
+
+RuleTester.setDefaultConfig({
+    parserOptions: {
+        ecmaVersion: 6,
+        ecmaFeatures: {
+            jsx: true
+        }
+    }
+});
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester();
+ruleTester.run("dropdown-needs-arialabeledby-and-label-v9", rule, {
+    valid: [
+        `<><Label id={comboId}>Best pet</Label> <Dropdown aria-labelledby={comboId} multiselect={true} placeholder="Select an animal" {...props} > {options.map((option) => ( <Option key={option} disabled={option === "Ferret"}> {option} </Option> ))}</Dropdown></>`,
+        `<><Label id={comboId2}>This is a Dropdown</Label><Dropdown aria-labelledby={comboId2} /></>`
+    ],
+    invalid: [
+        {
+            code: `<Dropdown multiselect={true} placeholder="Select an animal" {...props} > {options.map((option) => ( <Option key={option} disabled={option === "Ferret"}> {option} </Option> ))}</Dropdown>`,
+            errors: [{ messageId: "missingLabelOrAriaLabeledByInDropdown" }]
+        },
+        {
+            code: `<Dropdown aria-labelledby={comboId} multiselect={true} placeholder="Select an animal" {...props} > {options.map((option) => ( <Option key={option} disabled={option === "Ferret"}> {option} </Option> ))}</Dropdown>`,
+            errors: [{ messageId: "missingLabelOrAriaLabeledByInDropdown" }]
+        },
+        {
+            code: `<><Label>This is a Dropdown</Label><Dropdown aria-labelledby={comboId} multiselect={true} placeholder="Select an animal" {...props} > {options.map((option) => ( <Option key={option} disabled={option === "Ferret"}> {option} </Option> ))}</Dropdown></>`,
+            errors: [{ messageId: "missingLabelOrAriaLabeledByInDropdown" }]
+        },
+        {
+            code: `<><Label id="another-id">This is a Dropdown</Label><Dropdown aria-labelledby={comboId} multiselect={true} placeholder="Select an animal" {...props} > {options.map((option) => ( <Option key={option} disabled={option === "Ferret"}> {option} </Option> ))}</Dropdown></>`,
+            errors: [{ messageId: "missingLabelOrAriaLabeledByInDropdown" }]
+        }
+    ]
+});