Add cross-platform support to decky (#387)

* Import generic watchdog observer over platform specific import

* Use os.path rather than genericpath

* Split off socket management in plugin.py

* Don't specify multiprocessing start type

Default on linux is already fork

* Move all platform-specific functions to seperate files

TODO: make plugin.py platform agnostic

* fix import

* add backwards compat to helpers.py

* add backwards compatibility to helpers.py harder

* Testing autobuild for win

* Testing autobuild for win, try 2

* Testing autobuild for win, try 3

* Testing autobuild for win, try 4

* Create the plugins folder before attempting to use it

* Implement win get_username()

* Create win install script

* Fix branch guess from version

* Create .loader.version in install script

* Add .cmd shim to facilitate auto-restarts

* Properly fix branch guess from version

* Fix updater on windows

* Try 2 of fixing updates for windows

* Test

* pain

* Update install script

* Powershell doesn't believe in utf8

* Powershell good

* add ON_LINUX variable to localplatform

* Fix more merge issues

* test

* Move custom imports to main.py

* Move custom imports to after __main__ check 

Due to windows' default behaviour being spawn, it will spawn a new process and thus import into sys.path multiple times

* Log errors in get_system_pythonpaths() and get_loader_version() + 

split get_system_pythonpaths() on newline

* Remove whitespace in result of get_system_pythonpaths()

* use python3 on linux and python on windows in get_system_pythonpaths()

* Remove fork-specific urls

* Fix MIME types not working on Windows

backend/localplatform.py

@@ -0,0 +1,11 @@
+import platform
+
+ON_WINDOWS = platform.system() == "Windows"
+ON_LINUX = not ON_WINDOWS
+
+if ON_WINDOWS:
+    from localplatformwin import *
+    import localplatformwin as localplatform
+else:
+    from localplatformlinux import *
+    import localplatformlinux as localplatform