Move platform requirements to availability annotations (#348)

* Move platform requirements to availability annotations

Adding or raising the deployment platforms in the package manifest is a
SemVer major breaking change as consumers must also add or raise their
deployment platforms. This is a known limitation of SwiftPM.

Unforunately this means that it's very difficult for non-leaf packages
to adopt packages which declare their platforms in the manifest. Doing
so puts the brakes on adoption and ecosystem growth. For 'core' packages
like this one availability constraints should be expressed on
declarations rather than in the manifest.

This patch adds equivalent availability annotations to declarations
across the package and removes platforms from the package manifest.

* Address naming feedback

Fix memory leak in Lock (#331)

Fix a few typos (#329)

* [DOCS] fix typo: precicely → precisely

* [DOCS] fix typo: ever → every

* [DOCS] fix typo: AsyncBufferSequence, relative

Add support for `SWIFTCI_USE_LOCAL_DEPS` convention (#311)

To use this package in utils/build-script pipeline

Fix potential deadlocks when resuming a continuation while holding a …

…lock (#303)

* Fix potential deadlocks in zip

* Fix debounce

* Fix combineLatest

* Fix Channel

* Fix buffer

Make throttle underscored (#296)

# Motivation
During the discussion in #248 it became clear that the semantics of `throttle` are not 100% figured out yet.

# Modification
This PR is making `throttle` an underscored API for the upcoming 1.0.0 release. This gives us more time to investigate what exact semantics we want to have.

Rework availability for executor to avoid warnings (#288)

buffer: implement with custom storages (#239)

AsyncLazySequence proposal (#189)

Remove the disable of availability and mark methods as available to c…

…lock/instant/duration (#165)

* Remove the disable of availability and mark methods as available to clock/instant/duration

* Rework availability to be more permissive for tests

* Use hand coded values instead of defines (only available via Darwin versions of Dispatch)

* Adjust additional test availability

* Correct debounce test availability guard

* Update build instructions to indicate Xcode requirements

* Ensure the clock property of the validation diagram is only available for targets that can support it