build(meson): use python module instead of find_prog

This makes Meson use the internal Python version instead of looking for
the "python3" executable in the system.

This means that python will be more likely to be found on system where
the binary is named differently (Windows?), python3 is not required (any
version will do), and could even be faster.

meson.build

@@ -88,7 +88,7 @@ if meson.version().version_compare('>=0.57.0')
 else
 	# Ugly workaround for reading a file
 	version_data_raw = run_command(
-		find_program('python3'), '-c', 'print(open("version.txt").read())'
+		import('python').find_installation(), '-c', 'print(open("version.txt").read())'
 	).stdout().strip().split('\n')
 endif
 version_data_conf = configuration_data()