[clang-tools-extra] [clangd] Support symbolTags for document symbol (PR #113669)

[Dietrich Travkin via cfe-commits]

travkin79 wrote:

Thank you @chouzz for adding _Declaration_ and _Definition_ tags.

I'm sorry for answering late. I was quite busy last days.

Could we please also replace the _Const_ tag with the _Read-only_ tag? (I'm planning to remove the _Const_ tag from my PR on the LSP spec).

What about an [_Abstract_](https://en.cppreference.com/w/cpp/language/abstract_class) tag? Is there some clangd code that could be re-used for that?

https://github.com/llvm/llvm-project/pull/113669