Floss: Fork Floss D-Bus Clients from autotest_lib

Copied the following clients and utils from autotest_lib:
* adapter_client
* advertising_client
* scanner_client
* manager_client
* floss_enums
* observer_base

Changes made afterwards:
*Move all utils functions into one utils file.
*Remove qa_legacy_proxy calls from adapter_client.
*Lint the forked code as Google Python style.

Bug: 289480188
Test: mma packages/modules/Bluetooth
Tag: #floss
Change-Id: I3d32b3361b59255412bef9787a5258f73a6d28a9