[lexical-utils] fix: Backward selection was not being retained

[jvithlani]

Description

Problem
The selectionAlwaysOnDisplay utility wasn't working correctly for right-to-left text selections (when users drag from right to left). The visual selection mark would not appear properly when the editor lost focus after making a right-to-left selection.

Root Cause
The issue was in the rangeFromPoints function in markSelection.ts. The function was only checking focusNode.isBefore(anchorNode) to determine selection direction, which works for selections across different DOM nodes but fails for selections within the same text node.

For same-node selections:
Left-to-right: anchor.offset < focus.offset (e.g., 5 → 10)
Right-to-left: anchor.offset > focus.offset (e.g., 10 → 5)
The original logic didn't account for this offset-based direction detection.

Solution
Enhanced the selection direction detection logic to handle both cases:

Closes #7736

Before

Screen.Recording.2025-08-04.at.6.55.16.PM.mov

After

Screen.Recording.2025-08-04.at.9.32.03.PM.mov

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[jvithlani]

confirmed this fails on the main branch

[etrepum]

A simpler fix would be to use the isBackwards method of RangeSelection, e.g.

function $getOrderedSelectionPoints(selection: RangeSelection): [PointType, PointType] {
  // there's no reason for this to be nullable when called from RangeSelection, that could be fixed
  const points = selection.getStartEndPoints()!;
  return selection.isBackward() ? points.reverse() : points;
}

With this method to retrieve the anchor and focus, you could remove the broken direction code from rangeFromPoints altogether.

[jvithlani]

something like this @etrepum ?

[etrepum]

Yeah, this is what I was thinking, although not necessarily with all of the renaming (but that does make it clearer, so perfectly ok!)