* Adds RangeSet/DiscontiguousSlice to the stdlib
* Remove redundant DiscontiguousSlice.Index: Comparable conformance
* Attempt to fix embedded build
* Attempt to fix macOS test failures
* Fix Constaints/members.swift failure on linux
* Add exceptions to ABI/source checker to fix macOS tests
* Fix incremental dependency test failure
* Remove inlining/unfreeze implementation for future improvements
* Simplify indices(where:) implementation
* Address review feedback
* Add test for underscored, public slice members
* Address feedback on inlining, hashing, and initializing with unordered arrays
* Fix ABI checker issues
* Remove MutableCollection extension for DiscontiguousSlice
* Make insertion return a discardable Bool
* Fix ABI checker tests
* Fix other ABI checker tests due to dropping MutableCollection subscript
This adds the RangeSet and DiscontiguousSlice types, as well as collection
operations for working with discontiguous ranges of elements. This also adds
a COWLoggingArray type to the test suite to verify that mutable collection
algorithms don't perform unexpected copy-on-write operations when mutating
slices mid-operation.
