Enable path expansion in GCE modules

This is basically a replay of #16064 from `gce.py` to other pertinent
`gce_*.py` files. It enables expansions of paths in `gce.ini` like
`~/.project.json`

lib/ansible/modules/cloud/google/gce_net.py

@@ -329,8 +329,8 @@ def main():
             target_tags = dict(type='list'),
             state = dict(default='present'),
             service_account_email = dict(),
-            pem_file = dict(),
-            credentials_file = dict(),
+            pem_file = dict(type='path'),
+            credentials_file = dict(type='path'),
             project_id = dict(),
             mode = dict(default='legacy', choices=['legacy', 'auto', 'custom']),
             subnet_name = dict(),