Modify interactive inlay hints API to be more backwards compatible

[jakebailey]

This tweaks the API in #54734 to make it such that it's less likely to break consumers and require changes such as microsoft/monaco-editor#4100.

Unfortunately, this will require another vscode change to modify https://github.com/microsoft/vscode/pull/189344/files.

[typescript-bot]

Thanks for the PR! It looks like you've changed the TSServer protocol in some way. Please ensure that any changes here don't break consumers of the current TSServer API. For some extra review, we'll ping @sheetalkamat, @mjbvz, @zkat, and @joj for you. Feel free to loop in other consumers/maintainers if necessary.

[typescript-bot]

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page.

Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up.

[DanielRosenwasser]

CC @mjbvz

[jakebailey]

If we don't want to leave this blank, we'd need to drop the reassignment in the first branch, and then pull the code out of the second branch to make it unconditional. I.e., add the prop only when requested and everything else stays the same.

Happy to do whatever. Not sure which is better.