SoftInput flag requires focused View to show IME

Historically SOFT_INPUT_STATE_VISIBLE/SOFT_INPUT_STATE_ALWAYS_VISIBLE
have not required focused editor View [1] to work.  This is easy to
use, but also easy to tell IMEs to connect to InputConnection, which
is often recognized as a bug by users because often nothing happens
when the user taps the software keyboard.

This would become more obvious when we start allowing nothing to have
focus (Bug 68841055) in Android P.

Although how we should deal with "dummy InputConnection" is still an
open question, ignoring these SoftInput flags for apps that target P+
when there is no focused editor view is probably better than the
current behavior, where non-functional software keyboard is likely to
be shown.  The user is still able to show the IME by explicitly tap
the edit field.

As an implementation note, this CL trusts the targetSdkVersion
reported from the target application process, which is in general
unsafe.  That said, for this particular purpose it is acceptable.

 [1]: focused View that returns true from View#onCheckIsTextEditor().

Bug: 69256929
Test: atest CtsInputMethodTestCases
Test: atest FrameworksCoreTests:com.android.internal.inputmethod.InputMethodUtilsTest
Change-Id: I56682c7dee71d461687b9e80ab746d382fd55e0c