Handle whitespace inside #each with animation

[ehrencrona]

Fixes #5415: If there is stray whitespace inside an #each block that contains an animating element, strip the whitespace out during parsing. This makes sure that the check for whether there is only a single animating child passes.

I guess this means there's a risk that the semantics change subtly if animating inline blocks: you might expect them to be separated by whitespace but they won't be. On the other hand, since we don't support having more than one element animating it's kind of unavoidable. One could conceivably fix this by adding a <span> around the whole output, but I can't overview the consequences of that.

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

• 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
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[ehrencrona]

This was a while ago now, but can we merge? It feels like a fairly safe change.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ehrencrona]

@benmccann No worries. I rebased it now; seems to still work.

[benmccann]

Thanks for rebasing @ehrencrona. As a heads up, @tanhauhau had suggested discussing this PR at tomorrow's maintainer's meeting if you'd like to join

[ghostdevv]

This could possible fix/help fix #7124

[tanhauhau]

i've moved the test to a validator test to validate there's no compile error