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

[via cfe-commits]

chouzz wrote:

@travkin79 
Are you using the latesed commit? It works in my local clangd with given example.
```
I[11:05:17.623] --> reply:textDocument/documentSymbol(11) 3 ms
V[11:05:17.624] >>> {"id":11,"jsonrpc":"2.0","result":[{"detail":"const int","kind":13,"name":"g_var","range":{"end":{"character":19,"line":0},"start":{"character":0,"line":0}},"selectionRange":{"end":{"character":15,"line":0},"start":{"character":10,"line":0}},"tags":[21,20]},{"children":[{"detail":"void ()","kind":6,"name":"pub","range":{"end":{"character":14,"line":3},"start":{"character":4,"line":3}},"selectionRange":{"end":{"character":12,"line":3},"start":{"character":9,"line":3}},"tags":[19,5]},{"detail":"void ()","kind":6,"name":"pri","range":{"end":{"character":14,"line":5},"start":{"character":4,"line":5}},"selectionRange":{"end":{"character":12,"line":5},"start":{"character":9,"line":5}},"tags":[19,2]},{"detail":"void ()","kind":6,"name":"pro","range":{"end":{"character":14,"line":7},"start":{"character":4,"line":7}},"selectionRange":{"end":{"character":12,"line":7},"start":{"character":9,"line":7}},"tags":[19,4]}],"detail":"class","kind":5,"name":"P","range":{"end":{"character":1,"line":8},"start":{"character":0,"line":1}},"selectionRange":{"end":{"character":7,"line":1},"start":{"character":6,"line":1}},"tags":[20]}]}
```


And I am going to update the branch to remove `Constant`.


> Could you please check your implementation if the symbol tags are only created for diagnostics? If that's the case, could you please add symbol tags also for the following LSP methods and LSP types?

Currently, the implementation should only work in DocumentSymbol(outline). BTW, I tested in vscode, I am not sure why it also in `textDocument/publishDiagnostics`, could you please upload the full verbose logs of clangd? As for other features, I am going to add it after supported DocumentSymbol.

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