This patch implements `textDocument/semanticTokens/{full,range}`. If the
client supports semantic tokens, $ccls/publishSemanticHighlight (now
deprecated) is disabled.
These token modifiers are mostly useful to emphasize certain symbols:
`static, classScope, globalScope, namespaceScope`.
To enable a colorful syntax highlighting scheme, set the
highlight.rainbow initialization option to 10.
https://maskray.me/blog/2024-10-20-ccls-and-lsp-semantic-tokens
Note that the older $ccls/publishSemanticHighlight protocol with
highlight.lsRanges==true (used by vscode-ccls) is no longer supported.
