fix: add eslintrc files for check code convention

[Artxe2]

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---

1. Added eslintrc file to check snake_case.
ex) "$$" | "abc_abc", "__abc_abc", "$$abc_abc", "abc123", "abc_123" | "ABC_ABC", "ABC123", "ABC_123" | "AbcAbc", "Abc123", "Abc_123"
but the test folder was excluded because there were too many errors.

2. I modified the code according to the added eslint rule.
for public variable names, camelCase was applied using export as keyword or eslint-disable comment.

I'm not sure if this amounts to a large changes.

---

This PR has been force pushed,
including modifications to the regular expression in id-match and any additional changes that result from it.

check snake_case rule

1. $$
2. lower_snake_case that starts with a 0-2 letter _ or $
3. UPPER_SNAKE_CASE
4. PascalCase
5. Numbers can start with the second letter of each word. ex) a11y_required_attributes
6. It is possible to add a number with a hyphen at the end. ex) snake_case_123, PascalCase_123

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[benmccann]

we don't have a convention of aliasing external packages to snake_case

[Artxe2]

Yes, I understand.
If svelte 5 accepts the eslint rule,
You can use the eslint-disable-next-line id-match comment here.

[benmccann]

I appreciate that this rule found a lot of places that should be updated. However, I think it's just going to end up being too annoying to do eslint disable wherever we're calling an external package and think we probably can't accept this PR as a result. I really appreciate the effort you put into it. I think we could accept the fixes you identified if they were split out separately from the lint rule itself - though it might be better to wait until Svelte 5 for that as we're going to be throwing away all the existing compiler code

[Artxe2]

Thank you for the thorough review.
The changes were intended for validating the effectiveness of the rule, and I believe applying them in the current version wouldn't bring significant benefits.

[benmccann]

i'm not sure why these comments were removed

[Artxe2]

The return void is deduced automatically,
and I removed it because other parts of the code didn't add these type comments, but if it was a change to specify that nothing should be returned,
this change is should be roll back.

[benmccann]

thank you for this. it's a very interesting idea. unfortunately I don't think we can move forward for the reasons mentioned above: #9104 (comment)