Move ansible.galaxy.collection module into package

This change preserves how all the external imports refer to this code
while allowing us to start cutting the spaghetti into more easily
maintainable pieces.

This is a start of the upcoming refactoring effort destined to
eliminate tight coupling, implicit data manipulation, god objects,
abstraction leaks and other code smells.

Essentially, `ansible.galaxy.collection` is going to be a package that
holds parts of the collection management code spread across loosely
coupled modules.

PR: #71931

lib/ansible/galaxy/collection/__init__.py

@@ -1,5 +1,7 @@
+# -*- coding: utf-8 -*-
 # Copyright: (c) 2019, Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+"""Installed collections management package."""
 
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type

test/sanity/ignore.txt

@@ -37,7 +37,7 @@ lib/ansible/executor/powershell/async_watchdog.ps1 pslint:PSCustomUseLiteralPath
 lib/ansible/executor/powershell/async_wrapper.ps1 pslint:PSCustomUseLiteralPath
 lib/ansible/executor/powershell/exec_wrapper.ps1 pslint:PSCustomUseLiteralPath
 lib/ansible/executor/task_queue_manager.py pylint:blacklisted-name
-lib/ansible/galaxy/collection.py compile-2.6!skip # 'ansible-galaxy collection' requires 2.7+
+lib/ansible/galaxy/collection/__init__.py compile-2.6!skip # 'ansible-galaxy collection' requires 2.7+
 lib/ansible/module_utils/compat/_selectors2.py future-import-boilerplate # ignore bundled
 lib/ansible/module_utils/compat/_selectors2.py metaclass-boilerplate # ignore bundled
 lib/ansible/module_utils/compat/_selectors2.py pylint:blacklisted-name