[docs] refine load docs

[dummdidumm]

• split up the input properties into common, shared, server
• docs for RequestEvent
• code example for invalidation section
• better separate locals section in handle docs
• link back to load invalidation docs

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[theetrain]

Thanks for streamlining the docs! Once I re-read the final copy, I'll get a feel for how a developer can learn about all the loading and invalidation logic in order to build pages with predictable re-loads.

[Rich-Harris]

Docs are failing to deploy because the server-only load function doesn't yet include fetch. We could update the PR or (better) we could add fetch to RequestEvent

[dummdidumm]

I went the "adjust the example" route - the fetch thing would be nice, but feels too unrelated to this PR.

[geoffrich]

The term "shared-only" was confusing to me, since I don't think we use this term to refer to +page.js/+layout.js loads anywhere else. Is there something more descriptive?

[Rich-Harris]

I like 'universal load' but 'universal inputs' sounds like it applies everywhere. Given that the only one is data I wonder if the better solution is to restructure this section slightly instead

[dummdidumm]

One thing I realized which may make it so hard to structure this right is that we maybe approach this wrong in the first place. Right now most of this section reads like API reference, mixed with some context and explanations around it. I think it would be better to move much of this into the API section in a slimmed down version. This section should instead be crafted around the task people want to achieve - getting data into the page, how and when to update that data, when to use shared vs server load functions. We can probably reuse what's there already but not centered around the API (i.e inputs and output) but rather the problems and solutions.

[dummdidumm]

Created #7174 which "implements" my thoughts from the previous comment

[Rich-Harris]

closed via #7174