Validation rules: mismatch between graphql-js and spec

Context #3282 by @spawnia

It looks like we have the following mismatch between spec and graphql-js.
For example, type names are checked using this rule:
https://github.com/graphql/graphql-js/blob/main/src/validation/rules/KnownTypeNamesRule.ts

But in spec, there is only a rule for [checking type names on fragments](https://spec.graphql.org/draft/#sec-Fragment-Spread-Type-Existence) and I couldn't find any rule for checking types on variable fragments.
Also, we have a significant mismatch in names and descriptions of rules.

So at some point, we need to do an audit of both spec and graphql-js to fix as many discrepancies as we can.
We need to focus on query validation first and handle SDL validation separately since it's not well documented in the spec.