Add a enable/disable switch for using segmantation

By default, segmentation is turned off.
Note that there is an existing similar flag 'segmentation.enabled' under
SegmentationState struct under TileState, and the new one from this commit is
the master switch and later will be controllable by CLI.

By not using any segment, this temporarilly fixes the ongoing desync issues caused by quantizer rdo and
heuristic quantizer choice at speed 0,1,2.
12 jobs for pr-1923/ycho/rav1e/add_enable_segmentation_switch_in_FI in 31 minutes and 7 seconds (queued for 117 minutes and 26 seconds)
latest
Status Job ID Name Coverage
  Check
passed #9974
alpine docker
CAPI and Debugging Features

00:03:56

passed #9975
alpine docker
Compile Benchmarks

00:05:03

passed #9971
alpine docker
Latest Stable Rustc

00:09:01

passed #9972
alpine docker
Minimum Rustc

00:08:15

passed #9973
alpine docker
No Default Features

00:02:54

 
  Lint
failed #9976
alpine docker
Clippy Lints

00:01:25

passed #9977
alpine docker
Code Styles

00:00:31

 
  Build
skipped #9978
alpine docker
Build rav1e
 
  Test
skipped #9979
alpine docker
Coveralls Tests
skipped #9980
alpine docker
Slow Tests (aom)
skipped #9981
alpine docker
Slow Tests (dav1d)
 
  Doc
skipped #9982
alpine docker
Generate Docs
 
Name Stage Failure
failed
Clippy Lints Lint
   |
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unknown_clippy_lints

error: aborting due to 2 previous errors

error: Could not compile `rav1e`.

To learn more, run the command again with --verbose.
ERROR: Job failed: exit code 1