[Partial Screen Sharing] Fix color contrast of permission spinner arrow

The textColor attribute had no effect on the layer-list drawable item.
To fix it, we have to define the vector inline, and set the tint on the
vector.
Also took the liberty to use the same color attribute as used by the
QS arrow/chevron.

Fixes: 308369968
Test: Manual
Flag: None
Change-Id: I72591d57caaa7c0c4157d344747b1226919255ac