[tsserver] Support for "definitions" command (several definition)

[angelozerr]

Take a sample:

import {IFoldingRange} from 'vs/editor/contrib/folding/common/foldingRange';

export function computeRanges(): IFoldingRange[]

I would like when I do a Ctrl+Click on the last IFoldingRange that IDE provides 2 definitions:

• a definition with import {} (like today). Here Ctrl+Click on IFoldingRange[] select {IFoldingRange}
• a definition where IFoldingRange is exported. Here Ctrl+Click on IFoldingRange[] open "vs/editor/contrib/folding/common/foldingRange" file and select where IFoldingRange is exported.

So it should be cool if tsserver could provide "definitions" command to return this array of definition.

[RyanCavanaugh]

We now skip through imports and that seems to be broadly preferred