make all non-forking rvalue awaitables movable

[tzcnt]

The following rvalue-awaitable types have been made movable:

• mutex::lock_scope()
• mutex::co_unlock()
• mutex::co_unlock_return()
• semaphore::acquire_scope()
• semaphore::co_release()
• semaphoree::co_release_return()
• rw_lock::lock_read()
• rw_lock::lock_read_scope()
• rw_lock::lock_write()
• rw_lock::lock_write_scope()
• atomic_condvar::await()
• auto_reset_event::co_set()
• manual_reset_event::co_set()

The purpose of this is to make all of them safe to capture as a temporary into another awaitable group which wraps them into a task by taking them as an argument. When this happens, they will be bound as values, so their lifetime is the same as the task.

mux.fork<0>(rwlock.lock_read()); // implicit task wrapper
co_await mux.fork_clang<1>(tmc::as_task(sem.acquire_scope())); // explicit task wrapper

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After this, the only remaining non-movable rvalue-awaitables are those produced by an explicit fork primitive. For those, the rule remains as-before; you must assign them to a named variable before wrapping them into an awaitable group:

auto forked = tmc::spawn(some_task()).fork();
mux.fork<0>(std::move(forked));

(this fork behavior could be considered a footgun, and I'm considering making these lvalue awaitables, but that would be a substantial breaking change, so not today)