…onformances

…mances

Only asserts, not preconditions, as passing invalid indices here
cannot lead to out-of-bounds access — we have unconditional
bounds checks later.

This works slightly different as usual, as the input argument
specifies the maximum value we expect to store, not the maximum
count.

…se cases that require it.

This results in a significant speedup for both individual
insert/remove operations as well as bulk set operations -
up to 4x.

Use cases that require an O(1) count can use the separate
BitSet.Counted type.

…uirements

The two highlights are _customIndexOfEquatableElement and _customLastIndexOfEquatableElement, speeding up the implementation of `firstIndex(of:)` and `lastIndex(of:)`.

Add customary overloads for high-level Set operations.

Fleshing out `PersistentSet`

Rename `PriorityQueueModule` to `HeapModule`

[BitSet] Fix invariant violation in member subscript

It is not tenable to continue supporting ancient toolchains
indefinitely, as each supported toolchain version adds a nontrivial
amount of prerelease testing work. Additionally, working around
bugs in older toolchains that have been long since resolved is not a
productive use of anyone’s time.

Users who are stuck on older toolchains are of course welcome to
continue using the last package release that supports their
platform. (And they may continue to receive bug fix updates, as
we can always tag new bugfix releases on older minor release
branches.)

Unfortunate edge case: the new `initialize(fromContentsOf:)` from
SE-0370 is calling withContiguousStorageIfAvailable, so it is subject
to SR-14663.

This means we can either choose to continue maintaining the
workaround, or we can call the stdlib’s implementation, but not both.

[1.1.0] Bump minimum required Swift toolchain to 5.5

This is mostly about adding more type declarations to deal with type checker limitations in the older compiler.
This also includes workarounds that allow better support for CodingKeyRepresentable in PersistentDictionary, and it fixes a couple of small oversights on various #else branches.

Restore support for building with Swift 5.5

Merge release/1.0 to release/1.1

Update CMake configuration in preparation for 1.1

Remove accidental reference to CMakeLists.txt as a source file.

Update CMakeLists.txt