graphql-language-service: Support single-item coercion for lists

[AaronMoat]

https://spec.graphql.org/draft/#sec-List.Input-Coercion:

If the value passed as an input to a list type is not a list and not the null value, then the result of input coercion is a list of size one, where the single item value is the result of input coercion for the list’s item type on the provided value (note this may apply recursively for nested lists).

This allows inputs which accept one or many arguments (sometimes referred to as “var args”) to declare their input type as a list while for the common case of a single value, a client can just pass that value directly rather than constructing the list.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7b4bb82

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
graphql-language-service	Minor
codemirror-graphql	Patch

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.02%. Comparing base (0d9e51a) to head (7b4bb82).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...nguage-service/src/utils/getVariablesJSONSchema.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4090      +/-   ##
==========================================
+ Coverage   63.96%   64.02%   +0.06%     
==========================================
  Files          35       35              
  Lines        3086     3083       -3     
  Branches      948      946       -2     
==========================================
  Hits         1974     1974              
+ Misses       1107     1104       -3     
  Partials        5        5              

Files with missing lines	Coverage Δ
...nguage-service/src/utils/getVariablesJSONSchema.ts	1.62% <0.00%> (+0.03%)	⬆️

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