Change Overview Actions to round buttons.

If floating search is active in Overview (flag enabled and we are
the active Launcher), these buttons will be aligned to the search
bar relative to the bottom of the screen. Otherwise, the buttons
will be aligned below the active task like before.

Demo for Launcher3 build:
https://drive.google.com/file/d/1fVzRRnW5AFDMPkW-E8_w4BOCzTAOURQ_/view?usp=drive_link&resourcekey=0-6-EbFZXkBqcu0rw7uuEzjw

Bug: 292000892
Test: Manual with floating enabled/disabled and
SEPARATE_RECENTS_ACTIVITY enabled/disabled (simulating not being
the active Launcher). Also tested with a 3P Launcher, Nova.
Flag: N/A; this change is enabled by default, but also verified
UI looks correct with ENABLE_FLOATING_SEARCH_BAR.

Change-Id: Ia45f88d2c691c4525b1e73cca4707498d058a917