tokio-sync: add acquire_many and try_acquire_many methods to Sempahore

[dcarrier]

Fixes: #1550

Motivation

Add support for acquiring multiple permits on the Sempahore public api.

Solution

I changed the permits field type from u16 to u32 on Semaphore and OwnedSemaphorePermit to match the batch_semaphore lower level implementation which was introduced with #2607.

I added acquire_many and try_acquire_many methods to the Semaphore to add multiple permit acquisition functionality. I believe that these new methods have test coverage by the existing batch_semaphore tests.

[carllerche]

LGTM thanks.