invalidate $$props or $$restProps only when there's changes

[tanhauhau]

Fixes #4993
Fixes #5118

Before submitting the PR, please make sure you do the following

• It's really useful if your PR relates to an outstanding issue, so please reference it in your PR, or create an explanatory one for discussion. In many cases, features are absent for a reason.
• This message body should clearly illustrate what problems it solves. If there are related issues, remember to reference them.
• Ideally, include a test that fails without this PR but passes with it. PRs will only be merged once they pass CI. (Remember to npm run lint!)

Tests

• Run the tests with npm test or yarn test)

[Conduitry]

@tanhauhau What do you think about only including this extra check if the component uses $$props or $$restProps? In the js sample updates, I see a lot of cases where we're adding extra code for nothing. There's no reason to check is_empty($$props) if right after that we're checking 'foo' in $$props.

[tanhauhau]

I was thinking whether the early return can skip the rest of props dirty checking, but I guess less code is worth the trade off?

[Conduitry]

Yeah, I'm not sure. In cases where we just have the one prop being checked for, the extra is_empty check obviously only slows us down. This probably comes up more in tests than it comes up in real life components. I don't think we want to get into something like including the is_empty check if we have more than some number of in $$props checks later in the function.

In what sorts of situations might $set be called with {}? How often does that happen?

[tanhauhau]

In what sorts of situations might $set be called with {}? How often does that happen?

when a InlineComponent has dynamic attribute, it will always call the $set in the p function, even though there may be no changes.