zfree updates memory statistics. It gets the size of the buffer from
jemalloc by calling zmalloc_size. This operation is costly. We can
avoid it if we know the buffer size. For example, we can calculate
size of sds from the data we have in its header.

This commit introduces zfree_with_size function that accepts both
pointer to a buffer, and its size. zfree is refactored to call
zfree_with_size.

sdsfree uses the new interface for all but SDS_TYPE_5.

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

sdsalloc returns sds's length for SDS_TYPE_5. It's not correct for
SDS_TYPE_5.

This patch makes sdsAllocSize call zmalloc_size for
SDS_TYPE_5. sdsalloc is a lower level function that continues to
return length for SDS_TYPE_5.

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

Instead of zmalloc_size use s_malloc_size.

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

Change the doc string for `zfree_with_size`

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>