[browser][MT] dedicated io thread

[pavelsavara]

• dispatch Task resolve/reject to dedicated managed I/O thread and continuations to managed ThreadPool
• allow blocking .Wait on deputy thread in async methods, async JSExport, C# Main()
• keep throwing PNSE inside synchronous JSExport or callback

changes

• new JSThreadBlockingMode.AllowBlockingWaitInAsyncCode, make it default
• ToManaged(Task) creates Task with TaskCreationOptions.RunContinuationsAsynchronously
• mono_wasm_create_io_thread, mono_wasm_register_io_thread, mono_wasm_start_io_thread_async
• dispatch Promise/Task resolution to I/O Thread
• dispatch release_js_owned_object_by_gc_handle to I/O thread from UI thread
• call BeforeSyncJSExport and AfterSyncJSExport also on JSWebWorker (same thread)
• fix ConfigureAwait(true) in HTTP client
• add mono_wasm_print_thread_dump to INTERNAL

tests

• WaitDoesNotAssertInAsyncCode <-- this is why we do this!
• WaitAssertsOnSyncCallback
• WaitAssertsOnSyncJSExport
• _XUnitBackgroundExec not default, we don't need it anymore because blocking is fine!
• delete System.Runtime.InteropServices.JavaScript.BackgroundExec.Tests

new active issues

• [browser][MT] Some tests deadlock without -backgroundExec #99519
• [browser][MT] Deadlock in TaskCoverage.Coverage #99500
• [browser][MT] SemaphoreSlimTests.RunSemaphoreSlimTest1_WaitAsync_NegativeCases deadlock #99501

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

we have deadlock in

        public static void InitializationWithUriOnNonAsyncReaderThrows()
        {
            Assert.Throws<System.Net.Http.HttpRequestException>(() => XmlReader.Create("http://test.test/test.html", new XmlReaderSettings() { Async = false }));
        }

This is exactly the scenario that this PR should solve. It's synchronous Wait on fetch.
When I added bunch of Console.WriteLine in the code of XmlDownloadManager.GetStream it fixed itself.
I don't know why yet.

runtime/src/libraries/System.Private.Xml/src/System/Xml/XmlDownloadManager.cs

Line 23 in 18c3ad0

return GetNonFileStreamAsync(uri, credentials, proxy).GetAwaiter().GetResult();

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[maraf]

I'm missing change in dotnet.d.ts. Most of the comments are nits