libservo: Improve finding python (#33385)

* libservo: Improve finding python

Servo is built in a virtual environment, which sets `VIRTUAL_ENV` to
the base path of the venv.
PYTHON3 is only set if mach or the user set it.

Additional changes:

- Use Path / var_os for Paths instead of strings.
 In General using Path APIs is preferable, since in rare cases
 valid paths may not be valid utf-8.
- Don't search for python 3.8 anymore, since
  we require a newer version anyway.
- Don't add the .exe suffix anymore, since
  Command::new() will take care of that.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* script: Improve finding python

Synchronize `find_python` in scripts build.rs with the version in
libservo.

Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* Apply suggestions from code review

Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>
Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>

* Fix finding venv python on windows

- On Windows the venv scripts and python binaries are in the
  `Scripts` subdirectory instead of `bin`.
- We shouldn't check if the executable in the venv binary dir
  exists, since the actual file could have a `.exe` suffix.
  We don't need to consider the `.exe` suffix for the filename,
  since `Command` will handle that for us.
  We also anyway check the validity of the candidate file, by
  running `$candidate --version`.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
Signed-off-by: Jonathan Schwender <jonathan.schwender@huawei.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

0 files changed, 0 insertions, 0 deletions