Update validation page.

[mandiwise]

Description

This PR contains updated validation content for the Learn docs. Key changes include:

• New section that discusses how/when validation errors are returned to a client (note: I have a new "Response" page in development, and I will add a link on the validation page that points to the new page for more info when it's ready)
• Subheads for validation error examples to improve readability
• Light editing throughout

@benjie @jorydotcom

[vercel]

@mandiwise is attempting to deploy a commit to the The GraphQL Foundation Team on Vercel.

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[benjie]

This is looking good! Here are some light editorial suggestions (many of which apply to the original content).

[benjie]

Interested to know why you're moving away from the query shorthand here? It tends to be very rare that I see this - either the operation has a name and/or variables in which case you need query, or it has neither in which case it's very rare to see it in my experience.

[mandiwise]

I've tended to see the opposite (inclusion of the query keyword) so I included it for clarity after all of the keywords are introduced on the operation pages. But I can remove it throughout if the shorthand syntax is the preferred convention.

[benjie]

Let's worry about that afterwards, if at all; it's much easier to replace /^query {$/ with { than the reverse - so keep going with the query keyword for now.

Interesting that your experience differs; I wonder what the ecosystem as a whole sees!

[benjie]

Looks good to me! 🙌