Solution (#2366): Graph Editor: Add UI support for enumerated values

[TFGSUMIT]

This pull request adds UI support for enumerated values in the Graph Editor. It introduces a dropdown menu that displays enumerated values fetched from the /spec/definitions endpoint.

Changes:

• Added DropdownHelper class to fetch enumerated values and create dropdown menu options.
• Added DropHandling class to handle dropdown menu events.
• Updated Viewer class to initialize the dropdown menu and load enumerated values.
• Updated the Graph Editor's UI to display the dropdown menu.

Testing instructions:

1. Run the Graph Editor and navigate to the Enumerated Values section.
2. Select an enumerated value from the dropdown menu.
3. Verify that the shader generation system updates correctly.
4. Test the feature by selecting different enumerated values and verifying that the shader generation system updates correctly.

Note: This implementation assumes that the fetch API is available in the browser. If you are using a Node.js environment, you may need to use a different approach to fetch the enumerated values.

[linux-foundation-easycla]

• ❌ The email address for the commit (0ea0dfe, a8d6332, f5a64e6) is not linked to the GitHub account, preventing the EasyCLA check. Consult this Help Article and GitHub Help to resolve. (To view the commit's email address, add .patch at the end of this PR page's URL.) For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[kwokcb]

Hi @TFGSUMIT,
Thanks for taking a look into this.

Before continuing, can you elaborate on the need for a custom dropdown handler as:

1. lil-gui has support for this built in.
2. Users should never be allowed to dynamically add enumerations to inputs.

BTW, a change in enumerated string value will generally require a shader / material rebuild after setting it
on the MaterialX input.

[jstone-lucasfilm]

Thanks for diving into this, @TFGSUMIT! You can find instructions for resolving the EasyCLA error in the comment above.

[jstone-lucasfilm]

@TFGSUMIT As we have a Dev Days event next week, let us know if you'd like to continue working on this PR. If you're interested in continuing work on it, go ahead and add a comment to #2366, so that we can assign the task to you, and read the instructions in #3006 (comment) to resolve the CLA warnings above.

[jstone-lucasfilm]

I'll close out this PR for now, @TFGSUMIT, as it's still missing the authorization step we'd need to begin reviewing it, but feel free to take on another project for our upcoming Dev Days event!