[libzstd] Clean up parameter code

[libzstd] Clean up parameter code

* Move all ZSTDMT parameter setting code to ZSTD_CCtxParams_*Parameter().
  ZSTDMT now calls these functions, so we can keep all the logic in the
  same place.
* Clean up `ZSTD_CCtx_setParameter()` to only add extra checks where needed.
* Clean up `ZSTDMT_initJobCCtxParams()` by copying all parameters by default,
  and then zeroing the ones that need to be zeroed. We've missed adding several
  parameters here, and it makes more sense to only have to update it if you
  change something in ZSTDMT.
* Add `ZSTDMT_cParam_clampBounds()` to clamp a parameter into its valid
  range. Use this to keep backwards compatibility when setting ZSTDMT parameters,
  which clamp into the valid range.