feat(code/inlay): hide hints when selected by cursor

[saiintbrisson]

This PR closes #5903 (after almost a year 🥳, #5903 (comment)). You can enable the function to disable inlay hints inside text selections by setting rust-analyzer.inlayHints.hideWhenSelected to true.

[lnicola]

Oof, CC #11445.

[saiintbrisson]

Oh, that's unfortunate! Thank you for the heads up, should I close this?

[SomeoneToIgnore]

should I close this

Nobody knows for sure, I guess.

I would expect some people disappointed by the way the new hints work (see comments to the PR linked above), so we might keep our impl for a little longer?
Or not, if those issues are fixed or not that many people will actually care about the change.

But definitely it would be more beneficial to have less code to maintain ourselves, so we will abandon this code eventually.
First abandonment attempt will happen really soon (in the next Code version?), according to microsoft/vscode#16221 (comment)
So in perspective, this PR won't be used in the project at all and it might make sense to close it.

[saiintbrisson]

Will do, guess I should've done it sooner, but that's on me. Thank you anyway!