Preserve defaultValue literals (#3810)
[#3074 rebased on
main](https://github.com/graphql/graphql-js/pull/3074).
Depends on #3809
@leebyron comments from original PR (edited, hopefully correctly):
> Fixes #3051
>
> This change solves the problem of default values defined via SDL not
always resolving correctly through introspection by preserving the
original GraphQL literal in the schema definition. This changes argument
and input field definitions `defaultValue` field from just the "value"
to a new `GraphQLDefaultValueUsage` type which contains either (EDIT:
but not both!) "value" and "literal" fields.
>
> Here is the flow for how a default value defined in an SDL would be
converted into a functional schema and back to an SDL:
>
> **Before this change:**
>
> ```
> (SDL) --parse-> (AST) --coerceInputLiteral--> (defaultValue config)
--valueToAST--> (AST) --print --> (SDL)
> ```
>
> `coerceInputLiteral` performs coercion which is a one-way function,
and `valueToAST` is unsafe and set to be deprecated in #3049.
>
> **After this change:**
>
> ```
> (SDL) --parse-> (defaultValue literal config) --print --> (SDL)
> ```
Co-authored-by: Lee Byron <lee.byron@robinhood.com>
