Add new indexed_accessor_range_base and indexed_accessor_range classes that...

Add new indexed_accessor_range_base and indexed_accessor_range classes that simplify defining index-able ranges.

Many ranges want similar functionality from a range type(e.g. slice/drop_front/operator[]/etc.), so these classes provide a generic implementation that may be used by many different types of ranges. This removes some code duplication, and also empowers many of the existing range types in MLIR(e.g. result type ranges, operand ranges, ElementsAttr ranges, etc.). This change only updates RegionRange and ValueRange, more ranges will be updated in followup commits.

PiperOrigin-RevId: 284615679