Add hooks to configure system button text styling.

Add hooks to configure system button text styling.

Adds configuration values to change the styling of buttons on system
surfaces. Specifically, adds config_fontFamilyButton and
config_buttonTextAllCaps to control the default font and whether text
is all caps.

Additionally, adds plumbing so that these configs are utilized by
Theme.DeviceDefault (and descendent) themes. Some styles are added/updated
for this support.

Bug: 64122537
Bug: 69314526
Test: ag/3228846
Change-Id: I08406633bd744c6f58d5144d035aa27bf9c175df