Clean up post-migration TypeScript in @lwc/babel-plugin-component

[nolanlawson]

Follow-up from #3373. That PR just migrates the code to TypeScript, but there are further improvements we can make to both the code and the types.

E.g.:

• Use this.filename
• state.dynamicImports seems unused
• improve member expression computed typechecking

[nolanlawson]

We should also add JSDoc for these options:

lwc/packages/@lwc/babel-plugin-component/src/types.ts

Lines 13 to 21 in 767347b

	export interface LwcBabelPluginOptions {
	isExplicitImport?: boolean;
	dynamicImports?: {
	loader?: string;
	strictSpecifier?: boolean;
	};
	namespace?: string;
	name?: string;
	}

[nolanlawson]

Reopening as #3468 is a partial fix.