Clean up DocumentMessageHandler by breaking out several lengthy handlers into helper functions

[theaniketgiri]

Partly closes #2740

This PR addresses the "Match statements" section of the tracking issue by extracting three large match arms from process_message() into dedicated helper methods.

Changes

Extracted the following helper methods in DocumentMessageHandler:

Method	Lines Extracted	Purpose
handle_group_selected_layers	~50 lines	Handles layer grouping in both artboard and non-artboard workflows
handle_move_selected_layers_to	~85 lines	Handles layer movement with proper transform preservation
handle_nudge_selected_layers	~75 lines	Handles keyboard nudging with optional resize mode

Benefits

• Improved readability: The main match statement is now ~210 lines shorter
• Better maintainability: Each operation is now self-contained in its own method
• Easier testing: Helper methods can potentially be unit tested independently
• Clearer intent: Method names describe what the code does

Before/After

Before:

DocumentMessage::GroupSelectedLayers { group_folder_type } => {
    // ~50 lines of inline code
}

After:

DocumentMessage::GroupSelectedLayers { group_folder_type } => {
    self.handle_group_selected_layers(group_folder_type, responses);
}

Testing

• Verified compilation with cargo check
• Logic and behavior remain unchanged - this is a pure refactor
• Existing tests pass (note: SIGSEGV in tests is a pre-existing issue on master)

---

[timon-schelling]

Why the new workflow? That seems unrelated.

Converted to draft because this not ready for review.

[theaniketgiri]

Why the new workflow? That seems unrelated.

Converted to draft because this not ready for review.

Hi @timon-schelling, thanks for the review!

You're absolutely right - both the workflow file and pnpm-lock were accidentally included. They were from a different branch I was working on and got mixed in when I created this PR.

I've fixed this now:

Rebased onto master
Removed the unrelated workflow file and pnpm-lock
The PR now only contains the refactoring changes

[Keavon]

Hi @theaniketgiri, thanks again for this code contribution to the project! We're still hoping you will respond to the request to relicense this code. Please see #4208 ASAP, thank you!

[Keavon]

Hi @theaniketgiri, we're grateful of your past code contribution to Graphite, but unless we hear from you by the end of this weekend with agreement about relicensing your code to include the MIT license, we will begin steps to remove your code contributions so that you will no longer be a Graphite code contributor. We'd much rather avoid this outcome, so please respond now.

To agree, simply log into your GitHub account, visit #4208, and copy-paste this into a comment:

"I license my past and future contributions to Graphite under the dual MIT/Apache-2.0 license, allowing licensees to choose either at their option."

If you're hesitant because you disagree or have questions, feel free to respond with another message; we'll do our best to answer your questions or concerns. More explanation is at the top of the linked thread if you're confused. So far, 164 contributors have agreed and you are among the 11% remaining whom we are still hoping to hear from before we begin removing your code from the project starting this Monday. (If you only see this later than Monday, your future belated response will still be appreciated.)

Thank you for your cooperation and support of open source, and we hope you'll help us keep your valued contributions in-tact.