[Constraint application] Find trailing closure direction more carefully.

Rather than trying to include each expression kind, which leaves us
open to errors of omission, exclude only the case where we don't record
locators for trailing closure directions.

(cherry picked from commit cabcbc9)

Author: DougGregor

lib/Sema/CSApply.cpp

@@ -5703,7 +5703,7 @@ Expr *ExprRewriter::coerceCallArguments(
     SmallVector<LocatorPathElt, 4> path;
     auto anchor = locator.getLocatorParts(path);
     if (!path.empty() && path.back().is<LocatorPathElt::ApplyArgument>() &&
-        (isa<CallExpr>(anchor) || isa<SubscriptExpr>(anchor))) {
+        !isa<UnresolvedDotExpr>(anchor)) {
       auto locatorPtr = cs.getConstraintLocator(locator);
       assert(solution.trailingClosureMatchingChoices.count(locatorPtr) == 1);
       trailingClosureMatching = solution.trailingClosureMatchingChoices.find(