Adjust font and spacing inside CTA tile

Set button text size to 14dp to address
1) font size too small
2) text disappearing when scaled with font size settings
Also adjusted paddings to match spec.

Bug: b/346672101
Test: change font size in settings and verify CTA tile still
rendering to spec
Flag: com.android.systemui.communal_hub

Change-Id: Ia83b72bc3dafd02a16c4c5cab8339ebfb0dbf1c6