Add tests for MSC4155

[Half-Shot]

For element-hq/synapse#18288
This implements tests for matrix-org/matrix-spec-proposals#4155

Tests will not pass as I do not have rights to push to element-hq/Synapse, so it won't be able to find my branch.

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[anoadragon453]

The existing tests look great! Thanks for compiling these on top of Synapse's unit tests.

Could you add a few more sanity checks:

• A field present, but set to null, is treated as an empty array.
• A user being in both allowed_users and blocked_users should allow the user.
• Glob-style matching that uses a ? to represent a single character (spec)
• Escaping a glob works, so you can match a user with ID @*?:example.com (which is allowed under the historical user ID spec.

[Half-Shot]

Could you add a few more sanity checks

These are done, with the exception of Escaping a glob works, so you can match a user with ID @*?:example.com. There isn't a documented way to escape globs in Matrix yet, and I wouldn't want to introduce a test without spec backing it.

EDIT We agreed to ignore this for now, as matrix-org/matrix-spec#2156 is a problem.

[anoadragon453]

This now LGTM. Thank you for doing this!