Automatically listen to activetab (optionally?)

[fregante]

In some cases (most?) you'd also want the content script to be automatically available on the activeTab as well. This would avoid conflicting scripts trying to inject the script via different code paths:

• The content script is injected twice (editor open, click browser action) pixiebrix/pixiebrix-extension#3510

ActiveTab-tracking code can be found here and will likely be extracted, maybe into webext-tools:

• https://github.com/pixiebrix/pixiebrix-extension/blob/3d23b8063637aa5fd8734cabe7d3137cdd616c3a/src/background/activeTab.ts

On top of that, I think it also needs to listen to tabs and manually inject the scripts instead of relying on registerContentScripts. However it seems that the API supports activeTab in MV3: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/registerContentScripts

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To preserve the side-effects-only nature of the module, I think it can export an additional entry point:

import 'webext-dynamic-content-scripts/including-activetab';