compositeRefEnabled is an encoder only option. It should not be stored in the SPS.
This commit is the last to remove unused parameters from SPSNext. Thus also
all comments related to SPSNext are removed.

Started failing after merging !294

Clean-up of 2 parts in the ISP code that are redundant. The changes do not alter the performance in any way, i.e., the results are exactly the same.

1) In the full RD intra mode tests loop (estIntraPredLumaQT) there is the following condition:
    if ( uiOrgMode <= DC_IDX ) -> do X; else-> do X.
Since X is the same in both cases, the redundant code has been removed.

2) In xRecurIntraCodingLumaQT there is the threshold definition

double threshold = nSubPartitions == 2 ? 0.95 : subTuCounter == 0 ? 0.67 : subTuCounter == 1 ? 0.83 : 0.91;

Since subTuCounter can never be 0 (it is at least 1) at the time this expression is evaluated, the code has been simplified in the following way:

double threshold = nSubPartitions == 2 ? 0.95 : subTuCounter == 1 ? 0.83 : 0.91;

AMVR (formely IMV) now has only one mode, which used to be mode #2
- remove SPS imv_mode parameter
- remove encoder configuration for mode #1 (mode #2 replaces mode #1)
- adapt config files to refer tp mode #1
- rename SPS syntax elements and access functions to AMVR

Note: IMV to AMVR renaming in other parts of the software should be done by proponents.

  - Sub-PU TMVP can generate an invalid inter candidate.
  - Simplify previous solution and eliminate duplicated code.

When MC for luma only is desired, use existing luma/chroma parameters
instead of encoder-specific field in data structure

Also take care that luma only MC doesn't imply IBC

  - Fix overflow during reconstruction process.

- The M0297 zero-out is also supported for SBT now.
- The zero-out scanning code is moved out of residual_coding_subblock.

Deleted the TU retrieval from the DQP code in xCompressCU and the TU pointer being equal to nullptr check.

  - Sub-PU TMVP can generate an invalid inter candidate.

  - Triangle merge list zero-MV candidates not properly initialized.

Fix of the DQP signaling when there are multiple luma TUs in Single Tree and there is only one TU containing all of the chroma information

- fail to build when MSVC version too low
- properly identify clang as compiler

Dereferencing a nullptr should be avoided, even if the passed object is never used.
It may not be the most elegant solution to pass an empty list object, but it should work.

IBC block search history status is not reset for each frame, which may affect IBC searching results for the second frame.

- all elements of SPSNext are moved into SPS
- syntax elements of SPS are sorted according to draft (as far as possible)
- comments were added where software and draft diverge

- fix block statistics code for IBC mode after JVET_M0483_IBC
- enable build of block statistics code, when ENABLE_TRACING is specified on the command line

- removes old getIBCMode functions from SPSNext
- fixes references to this function in
  * reshaper
  * hash based ME

Note: SPSNext is going to be removed. Fixes can also be applied with the removal patch.