Add new semantic token types

The `decorator` type was introduced in LSP 1.17.
The `concept` type is used by clangd.

Author: bstaletic

python/ycm/semantic_highlighting.py

@@ -50,10 +50,12 @@
   'number': 'Number',
   'regexp': 'String',
   'operator': 'Operator',
+  'decorator': 'Comment',
   'unknown': 'Normal',
 
   # These are not part of the spec, but are used by clangd
   'bracket': 'Normal',
+  'concept': 'Normal',
   # These are not part of the spec, but are used by jdt.ls
   'annotation': 'Macro',
 }