Custom emmet snippets and issues with template languages

<!-- ⚠️⚠️ Do Not Delete This! bug_report_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- 🕮 Read our guide about submitting issues: https://github.com/microsoft/vscode/wiki/Submitting-Bugs-and-Suggestions --> <!-- 🔎 Search existing issues to avoid creating duplicates. --> <!-- 🧪 Test using the latest Insiders build to see if your issue has already been fixed: https://code.visualstudio.com/insiders/ --> <!-- 💡 Instead of creating your report here, use 'Report Issue' from the 'Help' menu in VS Code to pre-fill useful information. --> <!-- 🔧 Launch with `code --disable-extensions` to check. --> Does this issue occur when all extensions are disabled?: Yes. <!-- 🪓 If you answered No above, use 'Help: Start Extension Bisect' from Command Palette to try to identify the cause. --> <!-- 📣 Issues caused by an extension need to be reported directly to the extension publisher. The 'Help > Report Issue' dialog can assist with this. --> - VS Code Version: 1.57 - OS Version: win7 Steps to Reproduce: 1. Load up [repro repo](https://github.com/BassOfBass/vscode-emmet-repro). 2. Install recommended extensions. 3. Type `button` in the `index.jinja2`. 4. First issue is it will only show snippets from custom collection, but not the ones coming with VSCode. Although typing `button:s` will still yield `<button type="submit"></button>`, so it seems to be a display issue rather than snippet files override. 5. Also this disables all variations of snippets with `:`. Type `a:` and it won't suggest anything, even though `a:link` will work fine. 6. Go to `index.pug` and type `button`, it will show the default snippets, which means new snippets don't work. That's because I already had `"jinja-html": "html"` entry in the `"emmet.includeLanguages"` of workspace for jinja, so pug files require another entry. 7. Add `"jade": "html"` there (for whatever reason `"pug": "html"` doesn't work). 8. Emmet suggestion works now, with the…