fix(high contrast text): draw a solid rectangle background behind text instead of a stroke border

Bug: 186567103
Flag: com.android.graphics.hwui.flags.high_contrast_text_small_text_rect
Test: manual
1. adb shell setenforce 0 && adb shell setprop persist.device_config.aconfig_flags.accessibility.com.android.graphics.hwui.flags.high_contrast_text_small_text_rect true && adb shell stop && adb shell start
2. Settings -> Accessibility -> Display Size and Text
3. Turn on High Contrast Text

Change-Id: Ib2ef3925acc89b01c71addb63194d2a403c99cb6