TextEdit sometimes allocates extra space if text changes and no longer fits into previously allocated Rect.
It also can happen when rounding error occurs. In this case extra space is extra small.

If extra space is needed, Ui::allocate_rect is used to carve that space from placer.
However it always allocated extra space on the bottom-right from the rect placer returned initially.
This works well on Left-to-Right and Top-to-bottom layouts.
However in case it's Right-to-Left, Ui::allocate_rect updates placer's cursor and puts it to the right side of the initially allocated rect. And next widget is then placed over the TextEdit.

This is hard to notice usually.
However I have scaling that can cause rounding errors, so 0.0003 units of extra space is allocated each frame. Making next widget to overlap the TextEdit almost entirely.

This changes makes extra space allocation aware of the layout main direction and it picks most appropriate side of the widget for the extra space.

• Closes RTL layout breaks with TextEdit #5546
• I have followed the instructions in the PR template