Lagom: Add fuzz testing for LibJS using libFuzzer (#1692)

Note: clang only (see https://llvm.org/docs/LibFuzzer.html)

- add FuzzJs which will run the LibJS parser on random javascript inputs
- added a basic dictionary of javascript tokens

To use fuzzer:
CC=/usr/bin/clang CXX=/usr/bin/clang++ cmake -DENABLE_FUZZER_SANITIZER=1 ..
Fuzzers/FuzzJs -dict=../Fuzzers/FuzzJs.dict

Meta/Lagom/Fuzzers/FuzzJs.cpp

@@ -0,0 +1,14 @@
+#include <AK/StringView.h>
+#include <LibJS/Lexer.h>
+#include <LibJS/Parser.h>
+#include <stddef.h>
+#include <stdint.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    auto js = AK::StringView(static_cast<const unsigned char*>(data), size);
+    auto lexer = JS::Lexer(js);
+    auto parser = JS::Parser(lexer);
+    parser.parse_program();
+    return 0;
+}