Increase contrast of PIP menu controls

Increases the contrast of the PIP menu controls to comply with
accessibility requirements of minimum 3:1 contrast ratio.

As mentioned in b/309694613#comment6, we want at least 42% alpha.
Since we want keep to standardized alpha values, the closest one
is 54%.

Bug: 309694613
Flag: none
Test: manual check PIP menu is darker


Screenshots:
before - screen/A9wHp2aWKnrHwSN
after - screen/BYUJMdhjH37yFSN

Change-Id: I1fe27105f0fb8b2ef7cf30e857c90077fe8312bc