feat: add glimmer js/ts language

[IgnaceMaes]

• Format all commit messages with Conventional Commits
• I have read docs for adding a language.
• I have searched around and this is the most up-to-date, actively maintained version of the language grammar.
• I have added a sample file that includes a variety of language syntaxes and succinctly captures the idiosyncrasy of a language. See docs for requirement.

Adds support for .gjs and .gts file formats. Glimmer <template> tag components are the new format which power Ember.js. References:

• RFC: https://rfcs.emberjs.com/id/0779-first-class-component-templates
• Component implementation: https://github.com/ember-template-imports/ember-template-imports
• VS Code language definitions: https://github.com/chiragpat/vscode-glimmer

Local test:

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[octref]

Great work. Thank you 🚀