6.0: [MoveOnlyAddressChecker] Exclusivity handles DeadEnds.

[nate-chandler]

Explanation: Handle incomplete access scopes when diagnosing exclusivity issues.

The move-only address checker diagnoses exclusivity violations by checking whether consuming uses occur within an access scope (marked by one begin_access instruction and some number of end_access instructions). Specifically, it checks whether instructions that consume a value occur within the scope. If they do not, it emits an error.

In dead-end regions of a function (those from which there are no function exiting paths), special care must be taken when determining whether an instruction is live when the value which defines the region does not have a "complete lifetime" (a consuming use on every path). Access scopes do not always have complete lifetimes, so they need this special care. To get this special care, an instance of DeadEndBlocks must be passed to PrunedLiveness. (At the moment, it is also necessary to call areUsesWithinBoundary instead of isWithinBoundary, but that is only temporary.)

Here, the DeadEndBlocks instance is threaded a bit farther into the checker so that it can be passed along to PrunedLiveness.

The result is that consumes in dead-end blocks are correctly understood to be within the access scope when there is no end_access in that dead-end region.
Scope: Affects noncopyable code.
Issue: rdar://131960619
Original PR: #75404
Risk: Low. Amounts to passing an additional argument down in order to have an additional way to determine that an instruction is within a boundary. Furthermore, only affects the diagnostic relating to exclusivity emitted by the checker.
Testing: Added test.
Reviewer: Kavon Farvardin ( @kavon ), Joe Groff ( @jckarter )

[nate-chandler]

@swift-ci please test

[ktoso]

For tracking, this resolves #75312