Added special semantic coloring for consts, readonly properties, and enums.

[kronodeus]

This PR depends upon #80 because it requires semantic highlighting to be enabled.

The examples below demonstrate the changes to how constant/read-only tokens are colored. This is similar to how the modern built-in VS Code themes behave. Implementation taken from the Dark+ built-in theme. Colors taken from the original Gruvbox palette.

Before

After

[jdinhify]

@kronodeus looks like the change to overall semantics token in #83 affected how these look.

Could you please have a look again and see if you want to readjust 🙏

A suggestion is that try to use brighter colours to provide more contrast, the dark blue on dark background seems a bit lacking in contrast and make it somewhat hard to read as the result.

Bright colours for dark theme below

red2 fb4934
green2 b8bb26
yellow2 fabd2f
blue2 83a598
purple2 d3869b
aqua2 8ec07c
orange2 fe8019