Previously, both literal line feed characters in pre-formatted text and HTMl <br> elements returned a rect with 0 width and/or height.
Because of the way CharBounds() was implemented, this also returned 0 for x and y.
This caused problems for clients such as Windows Text Cursor Indicator which need the rectangle for the character at the caret.
Now, we return the correct x and y coordinates.
We also return a minimum width and height of 1 to ensure clients treat it as an actual rectangle.
As part of this, CharBounds() has been refactored slightly for consistency and readability.
As a bonus, this also fixes character bounds for list item bullets (bug 360003), but a test for that will be added in a subsequent patch.
This patch also removes the special case line feed code added to TextLeafRange::WalkLineRects() in bug 1946552, since CharBounds() now handles this.
Differential Revision: https://phabricator.services.mozilla.com/D249709
f66cf4466a