Cranelift: Add .wat to assembly test support and generate Wasm load/store tests for all ISAs (#5439)

* cranelift-filetest: Add the ability to test `.wat` to assembly

* Make the load/store test case generator script use `.wat` tests

And generate tests that exercise both Wasm-to-CLIF lowering and Wasm all the way
to assembly.

* Remove old versions of generated load/store tests

* Add new generated load/store tests

* Fix filename reference in script

cranelift/filetests/src/runner.rs

@@ -127,7 +127,7 @@ impl TestRunner {
         // This recursive search tries to minimize statting in a directory hierarchy containing
         // mostly test cases.
         //
-        // - Directory entries with a "clif" extension are presumed to be test case files.
+        // - Directory entries with a "clif" or "wat" extension are presumed to be test case files.
         // - Directory entries with no extension are presumed to be subdirectories.
         // - Anything else is ignored.
         //
@@ -160,7 +160,7 @@ impl TestRunner {
                                 // Recognize directories and tests by extension.
                                 // Yes, this means we ignore directories with '.' in their name.
                                 match path.extension().and_then(OsStr::to_str) {
-                                    Some("clif") => self.push_test(path),
+                                    Some("clif" | "wat") => self.push_test(path),
                                     Some(_) => {}
                                     None => self.push_dir(path),
                                 }