Synchronous Mutual Exclusion Lock (#2308)

* Pitch Mutex

Update nnnn-mutex.md

Updates to mutex

fix indents

more indent fixes

some more moot changes

Some updates from feedback

Mark a section as TODO

Remove lock, unlock, tryLock

Rewrite motivation and define differences between actors

Apply suggestions from code review

Co-authored-by: Konrad `ktoso` Malawski <[email protected]>

Remove reference to old free lock and unlock

Remove `@Sendable` on tryWithLockUnchecked

* Change tryWithLock to withLockIfAvailable

* Discuss disconnected as the future direction

* Update nnnn-mutex.md

* Discuss the transferring inout

Add link to transferring proposal

Fix spaces

Fix spaces

Add missing optional

Add missing optional

* Rename generic argument to State

* Fix Sendable extension and move it up

* Add toolchains

* Add note about toolchains not having transferring inout

* Update proposals/nnnn-mutex.md

* Update and rename nnnn-mutex.md to 0433-mutex.md

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Co-authored-by: Stephen Canon <[email protected]>

Author: Azoy