Relay M_TOKEN_INCORRECT as per MSC4183

[dbkr]

Relay error codes from the IS's submitToken endpoint

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[richvdh]

Copying some context from matrix-org/matrix-spec-proposals#4183 (comment) as to why this implements MSC4183:

• Synapse does not return a submit_url from any of the POST /_matrix/client/v3*/email/requestToken endpoints, so MSC4183 does not apply there.

• Synapse does not support POST /_matrix/client/v3/account/3pid/msisdn/requestToken (removed in Kill off half-implemented password-reset via sms matrix-org/synapse#6101)

• Both POST /_matrix/client/v3/register/msisdn/requestToken and POST /_matrix/client/v3/account/3pid/msisdn/requestToken use IdentityHandler.requestMsisdnToken.

  requestMsisdnToken sets submit_url to /_matrix/client/unstable/add_threepid/msisdn/submit_token (yes, the register endpoint uses the add_threepid callback).

  And /_matrix/client/unstable/add_threepid/msisdn/submit_token is updated by this PR.

[richvdh]

Note also: Synapse does implement POST /_synapse/client/password_reset/email/submit_token; however, that is used as a second stage after the GET endpoint (which shows an HTML page which posts back to itself). It is not used as a submit_url from POST /_matrix/client/v3/account/password/email/requestToken.