indexHint is an idl type defined in hint.idl

Currently it accepts BSONObj or String as valid BSON types and is represented as a BSONObj in code (by converting an IndexName represented in String into a BSONObj).

When working with hint type, it not always clear what exactly does the hint represent, an IndexName, IndexKeyPattern, or a NaturalOrderHint.

As part of SERVER-77075 query settings were defined in the idl, together with the index hint spec and the new definition of the (new) index hint type.

New IndexHint class is represented as a class wrapping 

stdx::variant<IndexKeyPattern, IndexName, NaturalOrderHint> _hint;

which documents all possible index hint types.

As part of this ticket we would:

• remove the old index hint definition in idl
• replace the old usage with the new definition (e.g. in find command)
• remove the no longer needed methods like isHintIndexKey() and hasInvalidNaturalParam()
• refactor the findIndexesByHint() (including early return once index is found for the given hint)
• refactor various methods in query_planner.cpp including hintMatchesNameOrPattern()
• refactor query_shape::extractHintShape()