Allow using sendEvent with a custom event type.

[Half-Shot]

This exposes the ability to send a custom event type outside of TimelineEvents for the purposes of sending events that are not part of the Matrix spec, but may be used for specific applications. This change simply exposes an overload for the existing function, and two tests to ensure the typings are valid.

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• [N/A] Sign-off given on the changes (see CONTRIBUTING.md).

[t3chguy]

The overload makes the strict type moot and open the door to typos, the preferable approach is type declaration merging like EW does. https://github.com/element-hq/element-web/blob/develop/src/%40types/matrix-js-sdk.d.ts#L47-L55

[Half-Shot]

Huh, TIL. That should probably be documented in some fashion, since this feels semi-common as a use case.

[richvdh]

Huh, TIL. That should probably be documented in some fashion, since this feels semi-common as a use case.

PRs to improve the documentation very much welcome 😇