vcs_tag custom command is run in source dir, but file objects provided are relative to build dir

[mar-v-in]

Describe the bug
When using vcs_tag with a custom command, the command is executed with current working dir set to the source directory. I guess that is intentional as it makes things easier when dealing with commands like git. However, when arguments provided in the command are file objects (which is needed if they should end up as a dependency), these file objects are passed as a path to the command, that is relative to the build directory (not the current working directory), thus the path is not found.

To Reproduce
meson.build:

project('test')
prog_python = import('python').find_installation()
vcs_tag(command: [prog_python, files('test.py')], input: 'test.in', output: 'test.out')

test.in:

VCS TAG: @VCS_TAG@

test.py

print("Test")

$ meson setup build
$ meson compile -C build
/usr/bin/python3: can't open file '<source root>/../test.py': [Errno 2] No such file or directory

Expected behavior
The file parameter should be provided relative to CWD at execution time, that is relative to the source directory, not the build directory. At the same time the dependency in the build.ninja file must remain relative to the build directory for ninja to correctly represent it.

system parameters
Meson 1.7.0 on Debian sid.