don't use assert() inside filament

assert() is now replaced by assert_invariant() which has the same
prototype and (currently) behaves the same than assert().

<assert.h> should not be used anymore, and is replaced by 
<utils/debug.h>, which is where assert_invariant() is found.

The main motivation for this is to be able to set a breakpoint on the
assertion as lldb doesn't handle abort() very well, and doesn't
permit to inspect the stack trace.

A secondary motivation is to be able (at some point) to enable 
assertions without necessarily doing a debug build.

libs/utils/src/debug.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "utils/debug.h"
+
+#include <utils/Panic.h>
+
+namespace utils {
+
+void panic(const char *func, const char * file, int line, const char *assertion) noexcept {
+    PANIC_LOG("%s:%d: failed assertion `%s'\n", file, line, assertion);
+}
+
+} // namespace filament