Reapply "Fix JSClosure leak (#240)"

[kateinoigakukun]

Seems like something wrong is happening in https://github.com/swiftwasm/JavaScriptKit/actions/runs/8659623850. I need stress test this before re-landing this.

This reverts commit 8780e5f.

[github-actions]

Time Change: +114ms (1%)

Total Time: 9,319ms

Test name	Duration	Change
Serialization/JavaScript function call through Wasm import	19ms	-4ms (19%)	👏

View Unchanged

Test name	Duration	Change
Serialization/JavaScript function call through Wasm import with int	15ms	-1ms
Serialization/JavaScript function call from Swift	99ms	+2ms (1%)
Serialization/Swift Int to JavaScript with assignment	330ms	+9ms (2%)
Serialization/Swift Int to JavaScript with call	939ms	+8ms (0%)
Serialization/JavaScript Number to Swift Int	303ms	-1ms
Serialization/Swift String to JavaScript with assignment	383ms	-0ms
Serialization/Swift String to JavaScript with call	976ms	-7ms (0%)
Serialization/JavaScript String to Swift String	3,622ms	+96ms (2%)
Object heap/Increment and decrement RC	2,620ms	+12ms (0%)

View Baselines

Test name	Duration
Serialization/Call JavaScript function directly	3ms
Serialization/Assign JavaScript number directly	2ms
Serialization/Call with JavaScript number directly	3ms
Serialization/Write JavaScript string directly	3ms
Serialization/Call with JavaScript string directly	2ms