meson: Re add workarounds to detect libpython path

This was removed all together in af4ade37
"meson: use new python module".

And add `-Dlibpython-dir` option for the cases the logic fails.
8 jobs for master in 19 minutes and 47 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #94218
gst indent

00:00:22

passed #94217
manifest

00:00:32

 
  Build
passed #94219
build fedora x86_64

00:03:37

 
  Test
passed #94220
check fedora

00:03:59

 
  Full Builds
passed #94221
build android arm64 api28

00:04:55

passed #94223
build cerbero cross win32

00:11:36

passed #94224
build cerbero cross win64

00:06:02

passed #94222
build cerbero fedora x86_64

00:09:56