[RFC] Export all validation rules directly

It's become relatively standard to create a whitelist or blacklist of validation rules, and reaching into the package per rule can get messy. This exports all the rules at the higher levels of submodule and module as well to make this easier.

For explaination of whitelist of blacklist:

```js
// Whitelist
import { specifiedRules, ScalarLeafs } from 'graphql';

// A ruleset which only runs one rule.
const whitelistRules = [ ScalarLeafs ];
```

```js
// Blacklist
import { specifiedRules, ScalarLeafs } from 'graphql';

// A ruleset which only runs all but one rule.
const blacklistRules = specifiedRules.filter(rule => rule !== ScalarLeafs);

// Note: the wrong way to do a blacklist would be to import and specify all
// but one rule. That's a whitelist and would fail to pick up any added
// validation rules that may be amended to spec in the future.
```

Author: leebyron

src/index.js

@@ -247,7 +247,36 @@ export type {
 export {
   validate,
   ValidationContext,
+
+  // All validation rules in the GraphQL Specification.
   specifiedRules,
+
+  // Individual validation rules.
+  UniqueOperationNames,
+  LoneAnonymousOperation,
+  KnownTypeNames,
+  FragmentsOnCompositeTypes,
+  VariablesAreInputTypes,
+  ScalarLeafs,
+  FieldsOnCorrectType,
+  UniqueFragmentNames,
+  KnownFragmentNames,
+  NoUnusedFragments,
+  PossibleFragmentSpreads,
+  NoFragmentCycles,
+  UniqueVariableNames,
+  NoUndefinedVariables,
+  NoUnusedVariables,
+  KnownDirectives,
+  UniqueDirectivesPerLocation,
+  KnownArgumentNames,
+  UniqueArgumentNames,
+  ArgumentsOfCorrectType,
+  ProvidedNonNullArguments,
+  DefaultValuesOfCorrectType,
+  VariablesInAllowedPosition,
+  OverlappingFieldsCanBeMerged,
+  UniqueInputFieldNames,
 } from './validation';
 
 

src/validation/index.js

@@ -8,4 +8,84 @@
  */
 
 export { validate, ValidationContext } from './validate';
+
+// Spec Section: "Operation Name Uniqueness"
+export { UniqueOperationNames } from './rules/UniqueOperationNames';
+
+// Spec Section: "Lone Anonymous Operation"
+export { LoneAnonymousOperation } from './rules/LoneAnonymousOperation';
+
+// Spec Section: "Fragment Spread Type Existence"
+export { KnownTypeNames } from './rules/KnownTypeNames';
+
+// Spec Section: "Fragments on Composite Types"
+export { FragmentsOnCompositeTypes } from './rules/FragmentsOnCompositeTypes';
+
+// Spec Section: "Variables are Input Types"
+export { VariablesAreInputTypes } from './rules/VariablesAreInputTypes';
+
+// Spec Section: "Leaf Field Selections"
+export { ScalarLeafs } from './rules/ScalarLeafs';
+
+// Spec Section: "Field Selections on Objects, Interfaces, and Unions Types"
+export { FieldsOnCorrectType } from './rules/FieldsOnCorrectType';
+
+// Spec Section: "Fragment Name Uniqueness"
+export { UniqueFragmentNames } from './rules/UniqueFragmentNames';
+
+// Spec Section: "Fragment spread target defined"
+export { KnownFragmentNames } from './rules/KnownFragmentNames';
+
+// Spec Section: "Fragments must be used"
+export { NoUnusedFragments } from './rules/NoUnusedFragments';
+
+// Spec Section: "Fragment spread is possible"
+export { PossibleFragmentSpreads } from './rules/PossibleFragmentSpreads';
+
+// Spec Section: "Fragments must not form cycles"
+export { NoFragmentCycles } from './rules/NoFragmentCycles';
+
+// Spec Section: "Variable Uniqueness"
+export { UniqueVariableNames } from './rules/UniqueVariableNames';
+
+// Spec Section: "All Variable Used Defined"
+export { NoUndefinedVariables } from './rules/NoUndefinedVariables';
+
+// Spec Section: "All Variables Used"
+export { NoUnusedVariables } from './rules/NoUnusedVariables';
+
+// Spec Section: "Directives Are Defined"
+export { KnownDirectives } from './rules/KnownDirectives';
+
+// Spec Section: "Directives Are Unique Per Location"
+export {
+  UniqueDirectivesPerLocation
+} from './rules/UniqueDirectivesPerLocation';
+
+// Spec Section: "Argument Names"
+export { KnownArgumentNames } from './rules/KnownArgumentNames';
+
+// Spec Section: "Argument Uniqueness"
+export { UniqueArgumentNames } from './rules/UniqueArgumentNames';
+
+// Spec Section: "Argument Values Type Correctness"
+export { ArgumentsOfCorrectType } from './rules/ArgumentsOfCorrectType';
+
+// Spec Section: "Argument Optionality"
+export { ProvidedNonNullArguments } from './rules/ProvidedNonNullArguments';
+
+// Spec Section: "Variable Default Values Are Correctly Typed"
+export { DefaultValuesOfCorrectType } from './rules/DefaultValuesOfCorrectType';
+
+// Spec Section: "All Variable Usages Are Allowed"
+export { VariablesInAllowedPosition } from './rules/VariablesInAllowedPosition';
+
+// Spec Section: "Field Selection Merging"
+export {
+  OverlappingFieldsCanBeMerged
+} from './rules/OverlappingFieldsCanBeMerged';
+
+// Spec Section: "Input Object Field Uniqueness"
+export { UniqueInputFieldNames } from './rules/UniqueInputFieldNames';
+
 export { specifiedRules } from './specifiedRules';