c/highlights : Add a tag for function parameters, global variables, and macro defines

[LeoBras]

Thanks for working on Zed, I am loving using it!
Few requests :)

In C, It would be awesome if we could have different colors for function parameters, global variables and macro defines!

Function parameters:

They are super useful to be easily spotted because we can track faster which parts of the function are being affected by the parameter. I have seen a request for python #17532, and it would look like this:

See how parameter b has a different color than variable i

Global variables:

Sometimes it's important (while you read functions) to make sure to know which variables are global, and which are local, for a very similar reason than function parameters. So it would be awesome to be able to select a color for those.

Sample code with bad color choice, but representing the idea: check a and b

Macro defines:

Telling macros apart from functions can also be very useful, and there are already ways of setting a color on the "#define" part, so it makes sense to match the color on the usage:

On "improved", macro's usage has the same color as it's define

Edit: Adding a new request:

Fade-out disabled code

On VSCode, when code is disabled by a #ifdef, we have the text being faded-out:

(somewhere in the project, CONFIG_SMP is defined, so the second line is disabled and faded-out)

Is there any chance the above features are possible to achieve?

Thanks!
Leo