Depfile / file list generation

[takase1121]

This comes up when implementing lite-xl/lite-xl#1802, where meson wasn't able to track what files that were installed by lpm, so it wasn't able to clean up correctly. Meson supports reading depfiles, which is essentially a Makefile rule describing the output and input. If lpm is able to generate a depfile, meson should be able to clean up the plugins properly.

The specification for depfiles can be found here:
https://cmake.org/cmake/help/latest/command/add_custom_command.html#grammar-token-depfile-rule

[adamharrison]

This could probably be done as part of an lpm plugin here: https://github.com/adamharrison/lite-xl-maintenance.

What exactly did you want the depfile to look like? Just basically a list of paths with colons at the end for everything created as part of the install command?