pills should use the same display name as message sender

[HarHarLinks]

Is your suggestion related to a problem? Please describe.
There is a discrepancy between the displayed names and pills across all elements currently:

Display names in pills are (re-)resolved based on the current (newest) room state, i.e. will be refreshed upon switching to another room and back. Message sender names are resolved based on the room state at the point in time the message was sent, i.e. are "historically accurate".

Describe the solution you'd like
Neither solution is perfect, but it seems obvious that both display names should match.

As to which one is the better choice see #16419.

Describe alternatives you've considered

• Use MXID: constant, but hard to make the connection to possibly drastically different display name.

Additional context

• [feedback required] use newest vs historical display name in chat history #16419
• MXID as fallbacks in fluffychat Message previews use mxid instead of display name when mentioning users #16262

[t3chguy]

Duplicate of #4677