fuzz: reorganise the path for existing oss-fuzz fuzzers

In order to provide a better organisation for oss-fuzz fuzzers and
to avoid top-level clustters in the git repository when more fuzzers
are introduced, move the existing fuzzer-related sources to their
own oss-fuzz/ hierarchy.  Grouping the fuzzers into their own
directory, separate their application on fuzz-testing from the core
functionalities of the git code, prvides better and tidier structure
the oss-fuzz fuzzing library to manage, locate, build and execute
those fuzzers for fuzz-testing purposes in future development.

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

oss-fuzz/fuzz-pack-idx.c

@@ -0,0 +1,13 @@
+#include "object-store.h"
+#include "packfile.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	struct packed_git p;
+
+	load_idx("fuzz-input", GIT_SHA1_RAWSZ, (void *)data, size, &p);
+
+	return 0;
+}