Move legacy device_tracker setup to a tracked task (#113715)

* Move legacy device_tracker setup to a tracked task

Legacy platforms are now loaded in a tracked task which
allows anything waiting on device_tracker (such as
a config entry that uses the device_tracker
platform) to proceed.

This also allows us to remove the workaround
of adding device_tracker to
hass.config.components in its setup

* tweak

* tweak

* fix tests

tests/components/device_tracker/test_init.py

@@ -310,6 +310,7 @@ async def test_entity_attributes(
 
     with assert_setup_component(1, device_tracker.DOMAIN):
         assert await async_setup_component(hass, device_tracker.DOMAIN, TEST_PLATFORM)
+        await hass.async_block_till_done()
 
     attrs = hass.states.get(entity_id).attributes