Preparation for PoS

[limebell]

Changes

• Added MaxGasPrice property to IActionContext interface and its implementations. [[Add max gas price to IActionContext #3762]]
• (Libplanet.Explorer) Added self field to NoteStateType. [[Add "self" field to NodeState query #3841]]
• (Libplanet.Action) Removed IFeeCollector interface
  and its implementations. [[Remove IFeeCollector and its implementation #3867]]
• (Libplanet.Action) Removed following methods from the
  IActionContext interface. [[wip: Introduce/gas tracer #3868]]
  • Removed IActionContext.UseGas(long).
  • Removed IActionContext.GasUsed().
  • Removed IActionContext.GasLimit().
• (Libplanet.Action) Added GasTracer static class. [[wip: Introduce/gas tracer #3868]]
• (Libplanet.Action) Added LastCommit property to IActionContext
  interface and its implementations. [[Preparation for PoS #3912]]

Bug Fixes

• A vote without validator power(or null) cannot be added to HeightVoteSet.
• Fixed an issue where the proposer could suggest a vote with null validator power.
• Suppressed some warnings caused by blank lines.