## What changes were proposed in this pull request?
`AggregateFunction` currently implements `ImplicitCastInputTypes` (which enables implicit input type casting). There are actually quite a few situations in which we don't need this, or require more control over our input. A recent example is the aggregate for `CountMinSketch` which should only take string, binary or integral types inputs.

This PR removes `ImplicitCastInputTypes` from the `AggregateFunction` and makes a case-by-case decision on what kind of input validation we should use.

## How was this patch tested?
Refactoring only. Existing tests.

Author: Herman van Hovell <hvanhovell@databricks.com>

Closes #16066 from hvanhovell/SPARK-18632.