[base-controller] Fix any usage in BaseControllerV1 (#3959)

## Explanation

- For runtime property assignment, use `as unknown as` instead of `as
any`.
- Change the types for `BaseControllerV1` class fields `initialConfig`,
`initialState` from `C`, `S` to `Partial<C>`, `Partial<S>`.
- Initial user-supplied constructor options do not need to be complete
`C`, `S` objects, since `internal{Config,State}` will be populated with
`default{Config,State}`.
- For empty objects, prefer no type assertions or `as never` (`never` is
assignable to all types).
- Fix code written based on outdated TypeScript limitation.
- Generic spread expressions for object literals are supported by
TypeScript: microsoft/TypeScript#28234

## References

- Closes #3715 

## Changelog

###
[`@metamask/base-controller`](https://github.com/MetaMask/core/pull/3959/files#diff-a8212838da15b445582e5622bd4cc8195e4c52bcf87210af8074555f806706a9)

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've highlighted breaking changes using the "BREAKING" category
above as appropriate

packages/base-controller/src/BaseControllerV1.ts

@@ -42,12 +42,12 @@ export class BaseControllerV1<C extends BaseConfig, S extends BaseState> {
   /**
    * Default options used to configure this controller
    */
-  defaultConfig: C = {} as C;
+  defaultConfig: C = {} as never;
 
   /**
    * Default state set on this controller
    */
-  defaultState: S = {} as S;
+  defaultState: S = {} as never;
 
   /**
    * Determines if listeners are notified of state changes
@@ -59,9 +59,9 @@ export class BaseControllerV1<C extends BaseConfig, S extends BaseState> {
    */
   name = 'BaseController';
 
-  private readonly initialConfig: C;
+  private readonly initialConfig: Partial<C>;
 
-  private readonly initialState: S;
+  private readonly initialState: Partial<S>;
 
   private internalConfig: C = this.defaultConfig;
 
@@ -76,10 +76,9 @@ export class BaseControllerV1<C extends BaseConfig, S extends BaseState> {
    * @param config - Initial options used to configure this controller.
    * @param state - Initial state to set on this controller.
    */
-  constructor(config: Partial<C> = {} as C, state: Partial<S> = {} as S) {
-    // Use assign since generics can't be spread: https://git.io/vpRhY
-    this.initialState = state as S;
-    this.initialConfig = config as C;
+  constructor(config: Partial<C> = {}, state: Partial<S> = {}) {
+    this.initialState = state;
+    this.initialConfig = config;
   }
 
   /**
@@ -128,21 +127,19 @@ export class BaseControllerV1<C extends BaseConfig, S extends BaseState> {
         ? (config as C)
         : Object.assign(this.internalConfig, config);
 
-      for (const [key, value] of Object.entries(this.internalConfig)) {
+      for (const key of Object.keys(this.internalConfig) as (keyof C)[]) {
+        const value = this.internalConfig[key];
         if (value !== undefined) {
-          // TODO: Replace `any` with type
-          // eslint-disable-next-line @typescript-eslint/no-explicit-any
-          (this as any)[key] = value;
+          (this as unknown as C)[key] = value;
         }
       }
     } else {
       for (const key of Object.keys(config) as (keyof C)[]) {
         /* istanbul ignore else */
-        if (typeof this.internalConfig[key] !== 'undefined') {
-          this.internalConfig[key] = (config as C)[key];
-          // TODO: Replace `any` with type
-          // eslint-disable-next-line @typescript-eslint/no-explicit-any
-          (this as any)[key] = config[key];
+        if (this.internalConfig[key] !== undefined) {
+          const value = (config as C)[key];
+          this.internalConfig[key] = value;
+          (this as unknown as C)[key] = value;
         }
       }
     }