We're now double-diagnosing some things that are caught by both
SILGen and static enforcement; we can fix that later, but I want to
unblock this problem first.
Static diagnostics now refer to the identifier for the variable requiring
exclusive diagnostics. Additionally, when two accesses conflict we now always
emit the main diagnostic on the first modifying access and the note on either
the second modifying access or the read.
The diagnostics also now highlight the source range for the expression
beginning the access.
Add a simple, best-effort static check for exclusive access for stored
class properties. For safety these properties must be checked dynamically,
also -- but we'll now diagnose statically if we see an obvious violation.
Add a SILLocation-based syntactic suppression for diagnostics of static
access conflicts on the arguments to the Standard Library's swap() free
function. We'll suppress for calls to this function until we have a safe
replacement.
