Enable to emit activation events on all language files

[iku12phycho]

Hello,

I'm using textlint processor plugin for new file format support. However, ActivationEvents is not emitted when it changed.

It is good if it is enable to emit activation events on all language files.

https://github.com/taichi/vscode-textlint/blob/79225a379b2e73ab227d6e862b99f0cc586c88e9/packages/textlint/package.json#L117-L131

Additionally, if your extension needs to be activated before any language is used, you can use the generic onLanguage activation event to ensure this:

"activationEvents": [
    "onLanguage"
]

https://code.visualstudio.com/api/references/activation-events#onLanguage