Apply "default unsafe" annotation across webputils

Import bounds_safety.h across all of webputils, with one exception being
dsp.h, since it's imported by webputils.h in one place. Also prepend
WEBP_ASSUME_UNSAFE_INDEXABLE_ABI to every webputil file to indicate to
the compiler that every pointer should be treated as __unsafe_indexable.

We also need to replace memcpy/memset/memmove with the unsafe variants
WEBP_UNSAFE_*, as memcpy/memset/memmove require bounded/sized pointers.

With this change, all of libwebputils (and libwebp) should build with
-DWEBP_ENABLE_FBOUNDS_SAFETY=true

Change-Id: Iad87be0455182d534c074ef6dc1a30fa66b74b6c

src/dsp/dsp.h

@@ -19,8 +19,11 @@
 #endif
 
 #include "src/dsp/cpu.h"
+#include "src/utils/bounds_safety.h"
 #include "src/webp/types.h"
 
+WEBP_ASSUME_UNSAFE_INDEXABLE_ABI
+
 #ifdef __cplusplus
 extern "C" {
 #endif