feat: allow usage of getContext() within $derived runes

[trueadm]

Closes #13493.

This PR allows the usage of getContext() inside $derived runes. Previously, you could use it, but only on init and not updates – and this inconsistency was unnecessary. We can make it work just like we do in other places.

One interested thing came about from this change – a bunch of our existing tests broke because they incorrectly did not pass is_runes internally as the derived never had access to the ctx which contained if we're in runes or not, meaning that they were not working correctly – so I had to fix them too.

[changeset-bot]

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Latest commit: 94e31a5

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

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[JonathonRP]

I should be able to use $derived(getContext(...)) without error of getContext needs to be in component initialization code, correct?

[trueadm]

@JonathonRP Where is your $derived located? Do you have a REPL?

[JonathonRP]

@trueadm let me see if I can make repl. I could be doing something wrong but I have a $derived that calls a function that accesses context with hasContext and/or getContext in a function and uses the from store to get current. again I'll see if I can make a repl.

if it helps it only happens during hmr, it's not an issue on startup or refresh it seems - using sveltekit

[JonathonRP]

@trueadm this is what I was able to do, it doesn't produce the error in the client console but it's very close to what I am doing - https://stackblitz.com/edit/sveltejs-kit-template-default-n4ftuvxm?file=README.md

I can share a screen shot and repo too if that helps more?