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ARROW-15089: [C++][Compute] Implement kernel to lookup a MapArray item for a given key

Implement a Scalar Kernel to lookup a value for a given key in a `MapArray`, whose type is an alias for `List(Struct(<key>, <item>))`

Todo:
- [x] Add more tests and combinations (Do suggest more)
   - [x] `null` maps
   - [x] empty maps
   - [x] `null` items
   - [x] `null` non-empty items
      Types tested:
      - [x] PhysicalIntegralArrowTypes
      - [x] DecimalArrowTypes
      - [x] BaseBinaryArrowTypes
      - [x] Boolean
      - [x] FixedSizeString
      - [x] MonthDayNanoInterval

- [x] Template Kernel

Things to consider:
- [x] Looking up `null` keys. (Null keys are not allowed)

Closes #12162 from dhruv9vats/arrow-15089-test

Lead-authored-by: Dhruv Vats <dhruv25vats@gmail.com>
Co-authored-by: Dhruv Vats <dhruv@Dhruvs-MacBook-Pro.local>
Signed-off-by: David Li <li.davidm96@gmail.com>