[wasm][debugger] Fix check for already loaded assemblies (#43747)

We send assembly loaded events to the proxy based off events from the
debugger engine. And we check that it isn't an assembly that was already
loaded. This check has a bug in computing the assembly name, from the
filename, which caused these events to be sent even for already loaded
assemblies.

src/mono/wasm/runtime/driver.c

@@ -213,7 +213,8 @@ mono_wasm_assembly_already_added (const char *assembly_name)
 
 	WasmAssembly *entry = assemblies;
 	while (entry != NULL) {
-		if (strlen(entry->assembly.name - 4) == strlen(assembly_name) && strncmp (entry->assembly.name, assembly_name, strlen(entry->assembly.name - 4)) == 0)
+		int entry_name_minus_extn_len = strlen(entry->assembly.name) - 4;
+		if (entry_name_minus_extn_len == strlen(assembly_name) && strncmp (entry->assembly.name, assembly_name, entry_name_minus_extn_len) == 0)
 			return 1;
 		entry = entry->next;
 	}

src/mono/wasm/runtime/library_mono.js

@@ -2365,9 +2365,6 @@ var MonoSupportLib = {
 		if (MONO.mono_wasm_runtime_is_ready !== true)
 			return;
 
-		if (!this.mono_wasm_assembly_already_added)
-			this.mono_wasm_assembly_already_added = Module.cwrap ("mono_wasm_assembly_already_added", 'number', ['string']);
-
 		const assembly_name_str = assembly_name !== 0 ? Module.UTF8ToString(assembly_name).concat('.dll') : '';
 
 		const assembly_data = new Uint8Array(Module.HEAPU8.buffer, assembly_ptr, assembly_len);