fix(HCT):Hide HCT background when the text is only whitespace

Bug: 385167023
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: I3289699b5fa7d4e5fb678d52b7f36de436a0543c