fix: correct center-aligned mode in AppbarHeader

[lukewalczak]

Summary

PR introduces a fix for center-aligned where the long title was overlapping with the rest of the content.

Before the fix:

After the fix:

ios one icon	ios two icons

android one icon	android two icons

Note: for the shorter title which fits in the header without truncating, with two icons on the right side, the title is a bit left-aligned.

ios one icon	ios two icons

android one icon	android two icons

Test plan

Tests updated.

[github-actions]

The mobile version of example app from this branch is ready! You can see it here

.