Fix compatibility issue with ESLint v9

[SegaraRai]

The context.getScope() function, removed in ESLint v9, was used in src/rules/no-child-traversal-in-connectedcallback.ts, causing an error when the rule was executed in ESLint v9.
This PR migrates the relevant part to the new context.sourceCode.getScope(node) and migrates other deprecated APIs such as getSourceCode() to the new API added in ESLint v8.40.0.

[43081j]

not sure how nicely typescript will play if you do this, but we could keep compatibility by doing this:

const sourceCode = context.sourceCode ?? context.getSourceCode();

what do you think?

this is also what eslint's docs suggest

[SegaraRai]

I have confirmed that SourceCode#getScope(node) , which was added in ESLint v8.37.0, is already used in util/ast.ts.
Thus, this PR only affects users who are using ESLint v8.37 through v8.39.
Since ESLint v8.40.0 has been released more than a year ago, I no longer expect many such users and prefer to keep the codebase simple instead.
Perhaps it should be mentioned in the release notes.

[43081j]

is the same true for sourceCode?

i.e. was it available the same amount of time

if so, you're right, we're probably fine

[SegaraRai]

Yeah, sourceCode was added in v8.40.0, which was released more than a year ago.
(SourceCode#getScope(node) was introduced in v8.37.0, so only users using v8.37.0 to v8.39.0 are affected.)