Feature request: A way to customize the list of buildtypes for `--genvslite`

The `--genvslite` flag makes it possible to generate a VS solution that can quickly switch between build configurations. But looking at the documentation, the list of configurations is hardcoded to match the Meson buildtypes (debug, debugoptimized, release, minsize).

It would be nice to have a way to customize this list. Perhaps, add a way to define custom build modes in `meson.build`, and use them for both `--genvslite` and as a way to quickly apply sets of compiler flags.

I'm new to Meson, so I apologize if I'm missing something.

Start by reading the --genvslite documentation and locating its implementation and the code that defines the current debug, debugoptimized, release, and minsize list. Compare how build options are represented and how compiler flags are applied. Done means a documented, tested design lets users customize the configurations used by --genvslite, with the requested behavior agreed and covered by tests.

Written by the indexing model from the issue text.