Switch version gate for fallback linespacing to P

Previously, no version was defined for Android P. Now that
I0a90033239081c583b10021cbc06d032e206beb4 defines it, we can switch
the version gate on the new fallback-based linespacing behavior of
TextView and Switch to it.

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: Id68ea4b26baa8a632d9f516083a73a0b8879513f
Fixes: 64648475