Detail
- Use correct precision of distortion based on input bit-depth during the derivation of the palette for lossless coding.
- Remove the unnecessary calculation of distortion during palette coding RD decision on lossless.

JVET-Q0503: encoder only improvement (4 items) of palette mode
JVET-Q0712: fix palette encoder issue at high QPs. Fix on top of the optimized table in JVET-Q0503.

  - Remove additional dead code.

1. enabling the encoder-side RD check of ISP mode when ACT is disabled at CU level
2. ACT intra RD code clean-up

Detail
- Fix the mis-alignment of rate and distortion during palette coding RD decision.
- Use different weights on luma component cost and chroma component cost.

- Fix for the case that uninitialized or invalid best cost values are referred during search candidate selection

1. indentation
2. function naming
3. Class declaration positions