presets: add support for macro expansion to includes

This feature adds support for macro expansion to preset includes.

Macro expansion in includes is quite usefull, if we want to use a library of presets that are shared/used across multiple projects, but we do not want to copy the presets in every project, or we do not want to use submodules.

Here is an example:

{
  ...
  "include": [
      "$penv{IDT_HOME}/cmake/presets/idt.json"
  ],
  ...
}

Currently it expands $penv{} only, because it is the only possible macro expansion during includes processing phase (done before any other processing).

Topic-rename: preset-includes-macro-expansion