Scoring applicable indexes

[sezruby]

ApplyHyperspace (#405) rule refactoring introduces a scoring function for each index application so that we could rank and select an index with higher performance benefit, if there are more than one applicable index.
With an initial version, it's implemented with simple scoring functions, but we will enhance it later.

JoinIndexRule - CoveringIndex

• for left child: 70 * (common bytes / source relation bytes)
  • (common bytes / source relation bytes) to consider Hybrid Scan overhead
• for right child: 70 * (common bytes / source relation bytes)
• Should be prior than FilterIndexRule - CoveringIndex

FilterIndexRule - CoveringIndex

• 50 * (common bytes / source relation bytes)
  • (common bytes / source relation bytes) to consider Hybrid Scan overhead