Adjust the layout of nav buttons in 3 button mode with task bar / nav bar unification

In nav bar, we assign layout weight 0.25:0.5:1(for home but the content width of home is set to 80dp):0.5:0.25 with a LinearLayout. Since we use a FrameLayout for taskbar (to support both folded and unfolded task bar), in this change we are matching the layout by manually calculating the width of each section (since we are already manipulating like so in different layoutters)

Bug: 230395757
Test: https://screenshot.googleplex.com/3P6vDrgb6geqTUm
Change-Id: I6ba201477621f173e42c5211fcc68b24e3022122