Fix IME shrunk by WindowTokenClient mis-detach

As CL[1] introduced WindowTokenClient for WindowProviderService (aka the
parent class of InputMethodService starts from CL[2]) as a token that
IME context can associate with the windowContainer of
the InputMethod window in server side. Like the activity context,
IME context can adopt configuration/resources update when the IME
window changed by display/window changes.

And, the IME context caller can also create another type of context
with wrapping IME context (i.e. calling createDisplayContext to create
a display context), that makes this context can be mixed the window
token of WindowProviderService since it's the base context.

However, the finalization of the context mixed WindowTokenClient
will detach the token when the attached context type is non-window
context, this action will mis-detach the token when it managed by
WindowProviderService.

So like SoftKeyboard previously using
createDisplayContext in CL[3] to workaround context resources issues,
will in-directly expose this mis-detach token issue as the above.

Beside, the handling of WindowTokenClient#{onConfigurationChange,
onWindowTokenRemoved} does not thread-safe since this is called from
IPC.

As the result, the fix is to ignore the check in ContextImpl#finalize
to not detach the token when it managed by WindowProviderService,
also make sure to post to the main handler when received
onConfigurationChanged/onWindowTokenRemoved in WindowTokenClient.

Note that this fix could help to resolve "The Window Context should
have been attached to a DisplayArea." exception if the token has been
detached as the above case that happens before the next
WindowProviderService#attachToWindowToken invoked.

[1]: I64a1614f32d097785915f6105b1813a929e0fe32
[2]: Ie565e30ed5dd3f2cfe27355a6dded76dc3adc14b
[3]: Ic592a1d2fb2da149220c8b503b522b3e864bcc77

Bug: 213118079
Bug: 211062619
Test: manual as steps:
1) adb install -r EditTextVariations.apk
2) adb install -r SoftKeyboard.apk
3) adb shell ime enable com.example.android.softkeyboard/.SoftKeyboard
4) adb shell ime set com.example.android.softkeyboard/.SoftKeyboard5
5) Enable screen auto-rotation
6) Launch EditTextVariations from launcher's shortcut
7) Tap the first EditText field to show IME
8) Rotate the device to the landscape mode
9) Expect the IME should not be shrunk

Change-Id: I7beb7a122af93e596239a36db62073233cea0726