[DevDocs] Improve documentation for hwnd_cache

[enricogior]

We need to improve the documentation for
https://github.com/microsoft/PowerToys/blob/master/src/common/hwnd_data_cache.h
and
https://github.com/microsoft/PowerToys/blob/master/src/common/hwnd_data_cache.cpp

Also consider renaming some methods:
get_window_and_path -> this function filters out the current window and if not filtered, it returns the ancestor window handle and path

get_window -> this function is identical to get_window_and_path but returns only the ancestor handle

[bzoz]

hwnd_data_cahce was removed, so this is obsolete