This adds parameter highlighting for reference parameters and defaulted
parameters. For example:
```cpp
auto strip_prefix_only(std::string& s,
Hidden_Homonym skip_hidden_homonym = {}) const
-> Affixing_Result<Prefix>;
```
Previously both parameters were only highlighted as variables.
- treat `restrict`/`_Atomic` like `const`/`volatile` => @keyword.storage.modifier
- highlight `unsigned int` as builtin => @type.builtin
- recognize `static_cast` and friends => @keyword
- `template` is a kind of entity like `typename` => @keyword.storage.type
- many declaration modifiers have nothing to do with storage/types
(explicit, friend, access specifiers, inline in C++) => @keyword
- fix floats highlighted as integer => @constant.numeric
