[Google Blockly] Customize variable dropdown options

[ajpal]

jira
Modeled largely after https://github.com/code-dot-org/blockly/blob/main/core/ui/fields/field_variable.js#L143, which was implemented by #7349

Adds a custom override class for Blockly.FieldVariable so that we can override dropdownCreate to add our custom rename options to the dropdown and onItemSelected_ to handle the logic for when the rename options are selected. I'm not sure why onItemSelected_ is a class method and dropdownCreate is not, but since that's the way it is in Blockly Core, I left it as is in the custom class.

Before

After

[maddiedierker]

@cat5inthecradle your question came through in an email, but isn't showing in the github UI for some reason:

Just curious, is ??? just your placeholder for a variable name, or does ??? have some specific meaning

"???" is the default placeholder for an unnamed variable. i can't remember if it's us or blockly that set this default

[cat5inthecradle]

@madelynkasula I forgot how to github today 😅. That answer's my question! Thank you.