Add better support for imports suggestion

When imports that are declared via addExtraLib are explicitly wrapped inside declare module then IntelliSense is actually very nice.
Following setup:

monacoEditor.languages.typescript.typescriptDefaults.addExtraLib("declare module 'test/file1' { export interface Test {} }", 'file:///node_modules/@types/test/file1.d.ts')
monacoEditor.languages.typescript.typescriptDefaults.addExtraLib("declare module 'test/file2' { export interface Test {} }", 'file:///node_modules/@types/test/file2.d.ts')

produces very nice auto-completion:

But if type definitions are missing explicit module wrapping as following:

monacoEditor.languages.typescript.typescriptDefaults.addExtraLib('export interface Test {}', 'file:///node_modules/@types/test/file1.d.ts')
monacoEditor.languages.typescript.typescriptDefaults.addExtraLib('export interface Test {}', 'file:///node_modules/@types/test/file2.d.ts')

then IntelliSense is also completely missing:

It would be nice if the latter use case would also produce the same outcome as the first one without needing to explicitly wrap type definitions.

Start by reproducing the two addExtraLib examples and comparing IntelliSense behavior for explicitly wrapped versus unwrapped declarations. Trace the import-suggestion handling used by Monaco's TypeScript integration; done means unwrapped type definitions produce the same import suggestions and completion behavior as wrapped definitions.