This will reduce noise in other PRs.

Test against Go 1.19 and lint only for the latest version.
Update to latest staticcheck to work with 1.19.

Adds CompareAndSwap and Swap methods to String, Error, and Value,
implemented by making use of Value.CompareAndSwap and Value.Swap
added in Go 1.17.

Following that, add CompareAndSwap to all other types with "CAS" methods
and deprecate CAS in favor of CompareAndSwap, since that's the convention
the standard library chose for these in Go 1.19.

Adds a Pointer[T] type that provide the same functionality as
Go 1.19's `sync/atomic.Pointer[T]` in both, Go 1.18 and 1.19.

In Go 1.19, this uses the standard library's implementation,
and in 1.18 our own custom implementation based on UnsafePointer.
For Go 1.17, even though it's now unsupported, this is a no-op.

Refs GO-1572
Resolves #115

Prepare a new release with the following changes:
v1.9.0...2ab21d8