Use fallback-based line spacing in TextView etc

In TextView and Switch, version-gate the use of
setUseLineSpacingFromFallbacks() to apps targeting Android P and
later for backward compatibility.

In internal widgets, ImageFloatingTextView and SubtitleView, always
turn it on, since there is no backward compatibility concerns.

Bug: 28963299
Test: bit CtsWidgetTestCases:android.widget.cts.CheckedTextViewTest
Test: bit CtsWidgetTestCases:android.widget.cts.EditTextTest
Test: bit CtsWidgetTestCases:android.widget.cts.SwitchTest
Test: bit CtsWidgetTestCases:android.widget.cts.TextViewTest
Test: bit FrameworksCoreTests:android.widget.TextViewTest
Change-Id: Icfe4e71ba26bbc6755ba12ddab72e6bf20b3ce25