Bring inlay hints out of "proposal" feature

[kaleidawave]

Looks like the inlay hints have been standardized of 3.17.0 https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#version_3_17_0

Could these cfg guards now be removed?

lsp-types/src/lib.rs

Lines 147 to 150 in 9e6b353

	#[cfg(feature = "proposed")]
	mod inlay_hint;
	#[cfg(feature = "proposed")]
	pub use inlay_hint::*;

Haven't looked into whether any other guards need to be removed?

[ebkalderon]

I've done precisely this in #255 along with other 3.17.0 features.