- 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.

Remove JEM_USE_INTRA_BOUNDARY and HEVC_USE_4x4_DSTVII

Use a single array with elements that comprise scan x position, y
position, and index into block instead of separate arrays.

Simplify array initialization code

Remove unused contexts and split intra mode contexts into luma and
chroma sets to align with text description

calculate and check shifts only when they are actually used

The integration of JVET_M0297_32PT_MTS_ZERO_OUT adds unnecessary code as
well as unnecessary processing in the encoder quantization process. -
The suggested change simplifies the code and avoids unnecessary
processing for the zero-out region.

The suggested changes fix the following two issues:

[1]
For blocks with width>32 or height>32, the scan created in initRom()
(file Rom.cpp) are only valid for the non-zero-out region. However, in
Rom::xInitScanArrays() (file DepQuant.cpp), the zero-out region is also
used. This has the effect that the array raster2id[] contains wrong
values. As a consequence, wrong neighboring positions cpos[] are derived.

Even though a previous fix (fix #161) ensures that the positions are
clipped to a value inside the subblock, these positions could still be
wrong. It is suggested to fix the issue by correctly considering the
zero-out regions for larger blocks (which is the actual source of the problem).

[2]
In State::updateStateEOS(..), the array m_absLevelAndCtxInit should be
set equal to zero if a skipped subblock is selected. Otherwise, it could
be possible lead to a usage of wrongs contexts for following transform
coefficients.

In Rom::xInitScanArrays()

Decoder analyser did not work. This corrects the problem, removes unused
entries and corrects the orders of strings vs enum list.