os/bluestore: New variant of bluestore_blob_t::release_extents

os/bluestore: New variant of bluestore_blob_t::release_extents

Created new variant of bluestore_blob_t::release_extents function.
Now the function takes range [offset~length] as an argument,
a simplification that allows it to have much better performance.

Created comprehensive unit test, tests 40k random blobs.
The unit test does not test for a potential case of having
bluestore_blob_t.extents that are not allocation unit aligned.

Signed-off-by: Adam Kupczyk <akupczyk@ibm.com>