provide more semantic token information + refactor and fixes

[Techatrix]

these changes had a visible effect depending on the theme used:

• whether or not something is a namespace, struct, union, etc. is now set with a TokenType instead of TokenModifiers
• container fields that are named after a keyword were previously highlighted like an identifier

fixes #843

Here is how the above changed have affected highlighting.

Before	After
VS-Code "Default Dark+"	VS-Code "Default Dark+"
VS-Code "Monokai"	VS-Code "Monokai"
Sublime Text 4 "Default Dark"	Sublime Text 4 "Default Dark"

[leecannon]

Few things that don't seem quite right.

These four should all have the same color (also happened to notice that #445 doesn't work any more)

Its weird that both usages of var_stdout have the same color but the same is not true of const_stdout

Edit: Okay, with the first one it seems like the color is due to whether zls is able to resolve the reference or not (std is resolved, builtin is not) as actually adding a module module changes its color to match std.

[Techatrix]

I've reverted the change about marking const declarations readonly and it now looks more consistent even though a bit less colorful.