Improve completions at `x <` (type arguments or less than)

TypeScript Version: master

Code

x < /**/

Expected behavior:

If x is a number or string, get completions for values.
If x is a function, get completions for types.

Actual behavior:

Get completions for both.

[mhegazy]

I think this is more of signature help. we used to have this in TS 1.0, but never rewrote the feature. the idea is it treats < like ( in a function call, and shows you the list of applicable type parameters. see commented out section inhttps://github.com/Microsoft/TypeScript/commit/102da2d80a83d340a8bbcdea3814c7f1b87dd944#diff-77414312b9c8809bd4ba9e31e0c5f940R8 for more context.

As noted by @sheetalkamat in #23632 (comment) there is a function isPossiblyTypeArgumentPosition that should be able to handle this.

Signature help part done in #24138