Repository: vscode
Issue: [html] Extensions using htmlLanguageParticipants don't activate vscode.html-language-features
Labels: html,debt

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Does this issue occur when all extensions are disabled?: Yes (apart from the extension I'm testing)

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- VS Code Version: `1.71.0` `784b0177c56c607789f9638da7b6bf3230d47a8c` `x64`
- OS Version: `5.19.7-arch1-1`

Steps to Reproduce:

1. Create an extension using htmlLanguageParticipants (you can see the code I'm using at samuelcolvin/jinjahtml-vscode#118)
1. Load that extension into a debug window
1. Open a language that has htmlLanguageParticipants enabled for it (I'm using `jinja-html`)
1. Notice that HTML language participant support is not working
1. Switch language mode to the `html` language provided by `vscode.html-language-features`, causing that extension to load
1. Switch back to a language using htmlLanguageParticipants
1. Notice that HTML language participant support is working now

It looks like the built in Handlebars extension may mitigate this by adding a language activation for handlebars to the package.json of the html-language-features extension but this seems hacky and probably not ideal for third party extensions.

**Ext Host Logs:**

On startup:
```
[2022-09-09 18:12:00.110] [exthost] [info] Extension host with pid 359485 started
[2022-09-09 18:12:00.110] [exthost] [info] Skipping acquiring lock for /home/matt/.config/Code/User/workspaceStorage/5f95745873455f863d9a75ba9df82c4a.
[2022-09-09 18:12:00.203] [exthost] [info] ExtensionService#_doActivateExtension vscode.microsoft-authentication, startup: false, activationEvent: 'onAuthenticationRequest:microsoft'
[2022-09-09 18:12:00.314] [exthost] [info] ExtensionService#_doActivateExtension vscode.debug-auto-launch, startup: true, activationEvent: '*'
[2022-09-09 18:12:00.318] [exthost] [info] ExtensionService#_doActivateExtension vscode.git-base, startup: true, activationEvent: '*', root cause: vscode.git
[2022-09-09 18:12:00.323] [exthost] [info] ExtensionService#_doActivateExtension vscode.ipynb, startup: true, activationEvent: '*'
[2022-09-09 18:12:00.351] [exthost] [info] ExtensionService#_doActivateExtension vscode.git, startup: true, activationEvent: '*'
[2022-09-09 18:12:00.497] [exthost] [info] ExtensionService#_doActivateExtension vscode.github, startup: true, activationEvent: '*'
[2022-09-09 18:12:00.550] [exthost] [info] Eager extensions activated
[2022-09-09 18:12:00.569] [exthost] [info] ExtensionService#_doActivateExtension vscode.emmet, startup: false, activationEvent: 'onStartupFinished'
[2022-09-09 18:12:00.611] [exthost] [info] ExtensionService#_doActivateExtension vscode.merge-conflict, startup: false, activationEvent: 'onStartupFinished'
[2022-09-09 18:12:00.659] [exthost] [info] ExtensionService#_doActivateExtension vscode.github-authentication, startup: false, activationEvent: 'onAuthenticationRequest:github'
[2022-09-09 18:12:00.747] [exthost] [warning] [vscode.emmet] Accessing a resource scoped configuration without providing a resource is not expected. To get the effective value for 'emmet.includeLanguages', provide the URI of a resource or 'null' for any resource.
```

When opening a Jinja HTML file:
_nothing new_

Switching to built in HTML language:
```
[2022-09-09 18:12:10.034] [exthost] [info] ExtensionService#_doActivateExtension vscode.html-language-features, startup: false, activationEvent: 'onLanguage:html'
```