fix(core): prevent multiple main module loading (#12128)

This commit fixes a problem where loading and executing multiple 
modules leads to all of the having "import.meta.main" set to true.

Following Rust APIs were deprecated:
- deno_core::JsRuntime::load_module
- deno_runtime::Worker::execute_module
- deno_runtime::WebWorker::execute_module

Following Rust APIs were added:
- deno_core::JsRuntime::load_main_module
- deno_core::JsRuntime::load_side_module
- deno_runtime::Worker::execute_main_module
- deno_runtime::Worker::execute_side_module
- deno_runtime::WebWorker::execute_main_module

Trying to load multiple "main" modules into the runtime now results in an
error. If user needs to load additional "non-main" modules they should use
APIs for "side" module.

runtime/examples/hello_runtime.rs

@@ -57,7 +57,7 @@ async fn main() -> Result<(), AnyError> {
   let mut worker =
     MainWorker::from_options(main_module.clone(), permissions, &options);
   worker.bootstrap(&options);
-  worker.execute_module(&main_module).await?;
+  worker.execute_main_module(&main_module).await?;
   worker.run_event_loop(false).await?;
   Ok(())
 }