docs: Update for 1.8.0 changes (TypeScript 5.5)

[kitten]

• Change references to @0no-co/graphqlsp to gql.tada/ts-plugin
• Add sections for alternative setup instructions to Installation page
  • Separate section for VSCode
  • New section for @0no-co/graphqlsp in TypeScript <5.5
• Simplify all references to GraphQLSP by referring to it as the "TypeScript plugin"
• Rephrase a couple of outdated terms ("introspection file" to "typings output file")
• Rephrase several sections to make it easier to understand the TypeScript plugin / type system relationship

This will still need some updates to the Introduction page. Currenty, I'm thinking that we may want to split the "How it works" section out, and remove the support section (maybe supplementing the latter with some additions to "Writing GraphQL")

The introduction page could generally maybe be a bit more engaging or interactive.

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Latest commit: 6e3cf649a901bee2b34bc86323348630d5567cd8

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