shortyuv: use absPartIdx for CU/TU part offset like everywhere else
yuv: add copyPartToPart* methods for recon RQT finalization

We're switching reconQt to be kept in pixels rather than shorts
search: fix 4:2:2 chroma tskip bit-cost estimation
search: rename tmpCoeff to coeffRQT, tmpShortYuv to reconQtYuv / resiQtYuv

Explain why these buffers are allocated to max CU size at every layer, fix a
few nits
search: rename a couple chroma intra helper methods
search: improve a variable name
search: reconYuv as ref
search: simplify initTrDepth
search: simplify RDO chroma intra coding, changes tskip outputs

Since the TU layers above tskip's 4x4 are not encoding their residual (they
only need distortion, not RD cost) there is no reason to try to preserve the
entropy coder state. This gives slightly better compression than
before, when tskip is enabled, and I believe it makes the code a lot more
maintainable.
search: give offsetSubTUCBFs a basic comment
search: rename methods that read coeff and recon from RQT struct at final depths

also reorder arguments and pass reconYuv as a reference
search: nit. splitted is not a word
search: remove tskip analysis out of luma chroma normal path
search: keep recon QT in pixels, instead of shorts

This changes outputs, apparently because SSE is now comparing fenc against the
clipped recon instead of the un-clipped recon. This was punishing residuals
which were close to the pixel dynamic range limits. The user never sees un-
clipped pixels, and external distortion metrics always use clipped recon, so
it makes sense to do the same here (never mind the obvious perf benefits)
search: improve comments and readability of residualTransformQuantIntra
search: avoid a context save at the last recursion depth
trim x265_emms(), try to only use prior to floating point operations
primitives: remove unused calcrecon primitive (assembly needs cleanup)
search: prevent warnings about unused bCheckSplit value
encoder: issue warnings and explicitly disable tskip or culossless if rd < 3

the analysis code is quite incapable of making these RDO decisions at these
RD levels. It's best that these tools never appear to be enabled at these RD
RD levels, and to explain why