Serialize variable IDs in procedure definitions

[rachel-fenichel]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide

The details

Resolves

Fixes #1642

Proposed Changes

Serialize and deserialize variable IDs for arguments in procedure definitions.

Reason for Changes

Dragging this block from the toolbox into the workspace failed.

The initial XML had no variable IDs, so the code to load the blocks in the flyout created a potential variable for "list" (and another potential variable for "x").

Dragging from the flyout to the workspace uses blockToDom, then domToBlock.

The serialization of the procedure definition block and its mutation did not include a variable ID, so a new variable was created (with a new ID).

The serialization of the "list" reference in the inner blocks did include a variable ID, which was the ID of the potential variable in the flyout.

This ID did not match the new ID of the parameter, so there was a crashing error.

Test Coverage

Tested on:

• Desktop Chrome

Additional Information

Dragged in the above block from the flyout.

[rachel-fenichel]

I'm also going to cherry-pick this into the release.