feat(scalar): add generics to scalars

[sibelius]

based on gtkatakura/fullstack-challenge@36cc105

and #1487
and #576
and #914

only 2 flow erros to fix

for the first one, we can do this

this.parseValue = config.parseValue || (value => (value: any): TInternal);

for the second one, we can add a type param to valueFromASTUntyped or try to type cast the function (not sure if this is possible)

[sibelius]

fixed this 2 issues

now, we got 20 more to fix

like this one:

if (isObjectType(parentType) || isInterfaceType(parentType)) {
          fieldDef = parentType.getFields()[fieldName];
        }

I think %checks refinements does not work well with generics

it does not recognize that parentType can't be null in this situation

[Neitsch]

I love strong typing! Thank you for looking into this :)

[Neitsch]

Should this be <*, *>?

[sibelius]

• is deprecated on flow type

[Neitsch]

Could you explain what the purpose of / difference between TInternal and TExternal is?

[IvanGoncharov]

Fixed by #3228