Deepan190703/fix .mtl

[deepan190703]

Fixes #3067

Changes:
Allowing .mtl file uploads in the p5.js Web Editor would ensure feature consistency between the editor and p5.js itself, reducing potential confusion for users.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes Enable .mtl File Uploads #3067

[raclim]

Thanks for working on this! I think this looks pretty good so far!

I think one additional change I would make is adding '.mtl' to where the different file formats are mentioned in the translations/locales files. Here's a screenshot of those files below, and I'm going to link the specific line in the english translations for reference too.

I think it should be fine as is, but I might also double check if the '.mtl' file needs a specific file mode besides 'text/plain' for the getFileMode() function in the Editor/index.js file.

[raclim]

Thank you for adding in the translations!

I think besides the comment I left in the index.js file, it would be best to remove the changes in the package.json and package-lock.json file—ideally we don't want any changes to these files.

[raclim]

I added in one minor change that resets the package-lock.json file to mirror the one in the main branch, but overall I think this is great! Thanks for working on this and for your contribution!