Block Editor: Fix the position of vertical add new block in RTL mode

[sunnyssr]

Description

Fix the position of add new block / block insertor in vertical orientation in RTL mode

How has this been tested?

Steps:-

1. Go to Settings
2. Switch your language to any RTL language
3. Go to Gutenberg editor.
4. Try inserting the block between two blocks.

Screenshots

Before:

After:

Types of changes

closes #30867

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

cc @Ryokuhi @youknowriad

Pull request which is related to this: #27860

[youknowriad]

This makes sense to me. Thanks a lot for the fix.