…n a mapped type (#80286)

This change adds a ToScriptField class with the expectation it will be subclassed based on the 
needs of each mapped type to produce a DocValuesField used by the scripting fields api. This is 
intended to replace the more generic return of ScriptDocValues.

The change made here only targets classes implementing the LeafNumericFieldData interface to 
keep the initial change smaller, but is also an example for how this would work for other types of 
LeafFieldData as well.

It starts with the fielddataBuilder method of each MappedFieldType (where the appropriate 
subclass of ToScriptField is specified) then passes through the IndexFieldData.Builder to the 
IndexData.load method. From here the generated LeafFieldData uses the 
ToScriptField.getScriptField method to generate the appropriate type of DocValuesField as 
required by the new scripting fields api.

This design seems like the best way to meet the requirements for the scripting fields api by 
allowing enough information to pass all the way to the LeafFieldData, but without directly 
coupling the LeafFieldData to a mapped type so that the separation remains. There is also a 
precedent already set for this design in the keyword field family that uses a scriptFunction to 
generate a ScriptDocValues of the appropriate type. ToScriptField would eventually replace 
scriptFunction.