chore: simplify updates

[Rich-Harris]

We can make our lives a lot simpler by replacing this...

$.text_effect(text, () => $.get(foo));

...with this:

$.render_effect(() => $.text(text, $.get(foo)));

That might seem like a step backwards, but after minification it's a very minor difference of 3 bytes...

-a(b,()=>c(d));
+a(()=>b(c,d(e)));

...and we're able to get rid of the text_effect function which minifies to 32 bytes (function a(b,c){d(()=>e(b,c()))}), and which involves more function calls and more stuff that needs to be warmed up. The same is true for other foo_effect functions like style_effect and class_toggle_effect and so on (with more to come, hence draft status).

Most significantly, it allows us to get rid of the distinction between 'singular' and 'grouped' updates in template.js:

// singular update, because `somefunction` could be expensive
-$.text_effect(text, () => somefunction($.get(x)));
+$.render_effect(() => $.text(text, somefunction($.get(x))));

// grouped updates, because we know these are cheap
$.render_effect(() => {
  $.text(text_1, $.get(y));
  $.text(text_2, $.get(z));
});

This results in a fairly substantial simplification of the compiler.

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• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
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• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

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