[Development] Qt 6 buildsystem support requirements

[Kevin Kofler]

I wrote:
> Bazel is still fairly new and adoption is low, especially in the Free
> Software world.

PS: In addition, https://bazel.build/ itself describes Bazel as "Beta". In 
particular, "Bazel is not yet covered by a deprecation policy, may be 
subject to backward-incompatible changes, and is missing some features."

I do not think relying on a beta build system that may change incompatibly 
at any time is a good idea.

        Kevin Kofler