* Send `didSave` notifications to clangd if it supports it
- Minor update to the LSP protocol for `didSave` and `colorProvider` to be more in line with the spec
- Only send color requests over to clangd if it supports it
Rationale for this change: clangd recently implemented didSave support,
it is used to rebuild preambles when the user edits a header file
referenced by an open file.
Change-Id: Ie6e2198bdeccb9d1b4083806c254475baadc2d2b