Beef up how qmk doctor works. (#7375)

* Beef up how `qmk doctor` works.

* improve the `git submodule status` parsing. h/t @erovia

* Fix whitespace and imports

* yapf

* Add documentation for the new doctor functionality

* Replace type_unchanged() with str()

* remove unused modules

* Update lib/python/qmk/cli/doctor.py

Co-Authored-By: Erovia <Erovia@users.noreply.github.com>

Co-authored-by: Erovia <Erovia@users.noreply.github.com>

lib/python/qmk/submodules.py

@@ -0,0 +1,71 @@
+"""Functions for working with QMK's submodules.
+"""
+
+import subprocess
+
+
+def status():
+    """Returns a dictionary of submodules.
+
+    Each entry is a dict of the form:
+
+        {
+            'name': 'submodule_name',
+            'status': None/False/True,
+            'githash': '<sha-1 hash for the submodule>
+        }
+
+    status is None when the submodule doesn't exist, False when it's out of date, and True when it's current
+    """
+    submodules = {}
+    git_cmd = subprocess.run(['git', 'submodule', 'status'], stdout=subprocess.PIPE, stderr=subprocess.PIPE, timeout=30, universal_newlines=True)
+
+    for line in git_cmd.stdout.split('\n'):
+        if not line:
+            continue
+
+        status = line[0]
+        githash, submodule = line[1:].split()[:2]
+        submodules[submodule] = {'name': submodule, 'githash': githash}
+
+        if status == '-':
+            submodules[submodule]['status'] = None
+        elif status == '+':
+            submodules[submodule]['status'] = False
+        elif status == ' ':
+            submodules[submodule]['status'] = True
+        else:
+            raise ValueError('Unknown `git submodule status` sha-1 prefix character: "%s"' % status)
+
+    return submodules
+
+
+def update(submodules=None):
+    """Update the submodules.
+
+        submodules
+            A string containing a single submodule or a list of submodules.
+    """
+    git_sync_cmd = ['git', 'submodule', 'sync']
+    git_update_cmd = ['git', 'submodule', 'update', '--init']
+
+    if submodules is None:
+        # Update everything
+        git_sync_cmd.append('--recursive')
+        git_update_cmd.append('--recursive')
+        subprocess.run(git_sync_cmd, check=True)
+        subprocess.run(git_update_cmd, check=True)
+
+    else:
+        if isinstance(submodules, str):
+            # Update only a single submodule
+            git_sync_cmd.append(submodules)
+            git_update_cmd.append(submodules)
+            subprocess.run(git_sync_cmd, check=True)
+            subprocess.run(git_update_cmd, check=True)
+
+        else:
+            # Update submodules in a list
+            for submodule in submodules:
+                subprocess.run(git_sync_cmd + [submodule], check=True)
+                subprocess.run(git_update_cmd + [submodule], check=True)