feat(high contrast text): update design treatment: rounded rects

We will leave out soft light for now, as it has some rendering issues
during animations and the overscroll stretch effect.

Bug: 369901146
Flag: com.android.graphics.hwui.flags.high_contrast_text_small_text_rect
Test: atest frameworks/base/core/tests/coretests/src/android/text/LayoutTest.java
Test: atest cts/tests/tests/uirendering/src/android/uirendering/cts/testclasses/TextViewHighContrastTextTests.kt
Change-Id: I36e6828b4763478f417053d71199fee4edf69edb