Improved near-lossless mode.

Compared to previous mode it gives another 10-30% improvement in compression keeping comparable PSNR on corresponding quality settings.

Still protected by the WEBP_EXPERIMENTAL_FEATURES flag.

Change-Id: I4821815b9a508f4f38c98821acaddb74c73c60ac
bit_reader.h: cosmetics: fix a typo

Change-Id: I1ba09124700b3120f18eb3705eb5ba805feb2ca0
mark some init function as being safe for thread_sanitizer.

introduces the macro WEBP_TSAN_IGNORE_FUNCTION

Change-Id: I3de2b6c1a2076fba4da7ae50322551e026b2082b
add code for testing random incremental decoding in dwebp

(protected with WEBP_EXPERIMENTAL_FEATURES flag)

Change-Id: I6cc2488810ce2ccd5d45882bd12f34a3d0c8eab8
WEBP_TSAN_IGNORE_FUNCTION: fix gcc compat warning

move the attribute to the front of the function to quiet clang warning:
GCC does not allow no_sanitize_thread attribute in this position on a
function definition

Change-Id: Ie4cc6e35a07bd00eab67d9cd6801bd2be9cfe676