Update analytics for Mention

[artcodespace]

Handover notes
This PR is part of a sequence of 4 PRs, currently in draft, that do the element web work to integrate the analytics work associated with this PR: matrix-org/matrix-analytics-events#80

The PRs are all around 90% there and most of them have tests setup and implemented, although perhaps these may need extending for coverage reasons. If you're going to try and extend the coverage, I warn you now that testing the autocomplete on the existing composer is not easy - spent about half a day on that and could not figure out how to do it. I think adding testing there may take quite a lot of effort for minimal return (plus I imagine it would be clear if the analytics on it were failing as there would be no use of mentions from the current composer according to posthog).

These branches and PRs were made in the following order:

• Update analytics for Composer events #11245
• Update analytics for FormattedMessage events #11246
• Update analytics for Mention #11265
• Update analytics for SlashCommands #11264

The first PR bumps the analytics repo and adds the Composer event tracking. Each subsequent PR adds a single analytic to both the rich text editor (both modes) and the current composer.

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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