[mlir] Fix use-after-move issues (#165660)

This patch addresses two use-after-move issues:

1. `Timing.cpp` A variable was std::moved and then immediately passed to
an `assert()` check. Since the moved-from state made the assertion
condition trivially true, the check was effectively useless. The
`assert()` is removed.

2. `Query.cpp` The `matcher` object was moved-from and then subsequently
used as if it still retained valid state. The fix ensures no subsequent
use for the moved-from variable.

Testing:
`ninja check-mlir`

mlir/lib/Query/Query.cpp

@@ -121,12 +121,13 @@ LogicalResult MatchQuery::run(llvm::raw_ostream &os, QuerySession &qs) const {
   Operation *rootOp = qs.getRootOp();
   int matchCount = 0;
   matcher::MatchFinder finder;
+
+  StringRef functionName = matcher.getFunctionName();
   auto matches = finder.collectMatches(rootOp, std::move(matcher));
 
   // An extract call is recognized by considering if the matcher has a name.
   // TODO: Consider making the extract more explicit.
-  if (matcher.hasFunctionName()) {
-    auto functionName = matcher.getFunctionName();
+  if (!functionName.empty()) {
     std::vector<Operation *> flattenedMatches =
         finder.flattenMatchedOps(matches);
     Operation *function =

mlir/lib/Support/Timing.cpp

@@ -319,7 +319,6 @@ public:
   void mergeChildren(AsyncChildrenMap &&other) {
     for (auto &thread : other) {
       mergeChildren(std::move(thread.second));
-      assert(thread.second.empty());
     }
     other.clear();
   }