feat: execution for fragment arguments syntax (#2)

* implement execution for fragment arguments syntax

Co-authored-by: mjmahone <mahoney.mattj@gmail.com>

* add directive test (#9)

* add directive test

* add failing test

add additional nested fragment test (#8)

Correct test and lint stuff

suggestions for execution (#11)

* introduce internal getVariableSignature utility

now extracted also to graphql-js PR, see graphql#4175

* execution suggestions

fixes execution to always use fragment variable when has the same name as an operation variable

previously, we were allowing an operation variable to be used if the fragment variable was not provided, and the field had no default. Now, we still use the fragment variable, and so the value is null.

this now correct logic allows us to significantly reduce the diff from main

adds additional test

* move getVariableSignature to execution

as it cannot be used by validation, which must collect all errors rather than fail with invalid type for signature

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Co-authored-by: mjmahone <mahoney.mattj@gmail.com>
Co-authored-by: Yaacov Rydzinski <yaacovCR@gmail.com>