Add the ability to move selected lines up and down

[Bogdan-Belogurov]

Description

This PR introduces two new methods to TextViewController:
moveLinesUp()
moveLinesDown()

These methods allow users to move selected lines of text up or down within the text view.

Related Issues

• ✨ Move selected lines up and down #259

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

I tested a 50k line file to compare performance in Xcode and CodeEdit.

Xcode	CodeEdit
xcode.50k.lines.mov	code.edit.50k.lines.mov

[Copilot]

Pull Request Overview

This PR adds the ability to move selected lines of text up or down within the editor via new controller methods, key bindings, and unit tests.

• Introduces moveLinesUp() and moveLinesDown() in TextViewController with undo grouping and selection updates.
• Binds Option+Command+[ and Option+Command+] to trigger the new line‐moving actions.
• Adds unit tests covering single‐line and multi‐line move operations.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
Tests/CodeEditSourceEditorTests/Controller/TextViewController+MoveLinesTests.swift	New tests for moving lines up and down in single and multi‐line selections.
Sources/CodeEditSourceEditor/Controller/TextViewController+MoveLines.swift	Implements moveLinesUp() and moveLinesDown() with undo grouping.
Sources/CodeEditSourceEditor/Controller/TextViewController+LoadView.swift	Adds key bindings for Option+Command+[ and Option+Command+].

Comments suppressed due to low confidence (1)

Tests/CodeEditSourceEditorTests/Controller/TextViewController+MoveLinesTests.swift:1

• Missing boundary‐condition tests: there are no tests verifying that moving the very first line up or the very last line down is a no-op.

// TextViewController+MoveLinesTests.swift

[thecoolwinter]

Awesome work, thank you!!