Update header color for all bubbles

Bubble stack view - after dark mode change, update expanded view header color for all bubbles

Previously, mContext.getColor(R.attr.colorAccent) updated header color in a hacky way:

colorAccent was *not* a color => ResourcesNotFoundException => all bubbles re-inflated with the correct new color

Bug: 123829494
Test: manual
Change-Id: I526d6f91d032b24424740d93c3eec7776c1e0c44