Use IME image API impl as fallback in TextViewOnReceiveContentCallback

A bunch of apps implement the keyboard image API (see
https://developer.android.com/guide/topics/text/image-keyboard).
When image support in augmented autofill is released, we'd like it to
work immediately in apps that have previously implemented the keyboard
image API, without having to wait for these apps to move to the new
unified content insertion API. To make this possible, this change adds
logic to call the keyboard image API (InputConnection.commitContent) if
the app implements it and if the app target SDK is <= S. This gives apps
a full Android release to upgrade to the new content insertion API
while augemented autofill will immediately be able to insert images
without any changes in apps that have implemented the keyboard image
API.

Bug: 163400105
Bug: 152068298
Test: Manual and unit tests
  atest FrameworksCoreTests:TextViewOnReceiveContentCallbackTest
  atest CtsWidgetTestCases:TextViewOnReceiveContentCallbackTest
Change-Id: I9280604e7ec7e8d08c1179e6bbf0068647a41040