Update imports on file move rewrites `./index` to '.'

[mjbvz]

From microsoft/vscode#54981 (comment)

TypeScript Version: 3.1.0-dev.20180726

Search Terms:

• update imports
• getEditsForFileRename

Code
For a project

index.ts

export const foo = 123

foo.ts

import { foo } from './index';

1. In VScode, Rename foo.ts to bar.ts
2. Confirm that you want to update import paths

Expected behavior:
No edits returned from getEditsForFileRename

Actual behavior:
An edit is returned that rewrites foo.ts to:

import { foo } from '.';

We could add this as a new UserPreferences property: readonly importIndexPreference: "omitIndex" | "includeIndex";.

[mhegazy]

What should the default be?

[mjbvz]

My expectation as a user is that we don't touch the import in this case. If it's './index' leave it as './index' and if its '.' leave it as '.'

[jdforsythe]

@Andy-MS @mhegazy I think it should be: readonly importIndexPreference: "omitIndex" | "includeIndex" | "noChange";

where "noChange" is the default. Then users could opt in to always or never include index, but the default is to not change existing imports.

Normally we omit it, but for a particular module we only allow importing through the index file (due to some registration that happens) so the lint rule requires index to be present for this particular import.