Codec2: cleanup C2Param and C2Buffer API naming style

const static fields and enum values are UPPER_CASE and
  usually contain a prefix
private members are _mCamelCase
integral types are lower_case_t
other types are CamelCase

Also tweaked some names (added shift and endianness to C2PlaneInfo)
Renamed C2PlaneLayout to C2PlanarLayout
C2Param::indexFlags to PARAM_TYPE
C2Param::ParamIndex to type_index_t
C2Param::_paramIndex() to typeIndex()
C2Param::_coreIndex() to coreIndex()

Added equality operators to C2Param::BaseIndex and sub-classes

Bug: 64121714
Change-Id: I051a2c2fd9e896c64124cde2a385a93e7ee04951