[ConstraintSystem] Rename solveIteratively to solve and start using it

Remove solution filtering from new iterative `solve` method, and
replace all usages of `solveRec` with it.

lib/Sema/ConstraintSystem.cpp

@@ -2072,7 +2072,7 @@ bool ConstraintSystem::salvage(SmallVectorImpl<Solution> &viable, Expr *expr) {
     state.recordFixes = true;
 
     // Solve the system.
-    solveRec(viable);
+    solve(viable);
 
     // Check whether we have a best solution; this can happen if we found
     // a series of fixes that worked.