Hide Quick Settings shade when the FontScalingDialog is opened

When the users try to modify the font size through the Quick Settings,
we would like to hide the QS shade so users could see the text content
upderlying when they are modifying the font scale.

We consider the following cases:
1. Screen unlocked: hide the shade and show the dialog
2. Screen locked: dismiss keyguard, hide the shade, and show the dialog

Bug: 282110776
Test: manually - attach video to the bug
Test: atest FontScalingTileTest
Change-Id: I66a1c6b5df903c671b4b9c0eab178c5b6de99d61