Make lists consistently ordered in generate_meson_files.py

[CnlPepper]

When executing the generate_meson_files.py script, almost all meson.build files were modified, which seems to reorder the elements of the source files lists.
The pathlib.Path.iterdir() here:

source/dev/generate_meson_files.py

Line 197 in 5897707

for child in path.iterdir():

couldn't return a path object in a fixed order. (It perhaps depends on the OS platform?)
To consistently yield the same result without any source change, we likely need a workaround, such as using sorting or globbing.

Originally posted by @munechika-koyo in #419 (comment)