Add WebWorkerDedicatedExecutor to run actors on a dedicated web worker

[kateinoigakukun]

This PR introduces WebWorkerDedicatedExecutor, a new serial executor that runs on a dedicated Web Worker thread. This executor allows actors to run in their own isolated execution environment and provides an easier way to offload works.

actor MyActor {
    let executor: WebWorkerDedicatedExecutor
    nonisolated var unownedExecutor: UnownedSerialExecutor {
        self.executor.asUnownedSerialExecutor()
    }
    init(executor: WebWorkerDedicatedExecutor) {
        self.executor = executor
    }
}

let executor = try await WebWorkerDedicatedExecutor()
let actor = MyActor(executor: executor)

[github-actions]

Time Change: +523ms (5%) 🔍

Total Time: 10,095ms

Test name	Duration	Change
Serialization/JavaScript function call through Wasm import	26ms	+2ms (6%)	🔍
Serialization/JavaScript function call through Wasm import with int	23ms	+2ms (6%)	🔍
Serialization/JavaScript function call from Swift	136ms	+15ms (11%)	⚠️
Serialization/Swift Int to JavaScript with call	1,020ms	+59ms (5%)	🔍
Serialization/JavaScript Number to Swift Int	292ms	+22ms (7%)	🔍
Serialization/Swift String to JavaScript with assignment	440ms	+24ms (5%)	🔍
Serialization/Swift String to JavaScript with call	1,103ms	+62ms (5%)	🔍
Serialization/JavaScript String to Swift String	3,873ms	+288ms (7%)	🔍

View Unchanged

Test name	Duration	Change
Serialization/Swift Int to JavaScript with assignment	352ms	+16ms (4%)
Object heap/Increment and decrement RC	2,812ms	+30ms (1%)

View Baselines

Test name	Duration
Serialization/Call JavaScript function directly	3ms
Serialization/Assign JavaScript number directly	4ms
Serialization/Call with JavaScript number directly	3ms
Serialization/Write JavaScript string directly	4ms
Serialization/Call with JavaScript string directly	4ms