refactor: Add default implementation for WorkerOptions (#14860)

This adds an implementation of `Default` for both `WorkerOptions` and
`BootstrapOptions`. Since both of these structs are rather big, this
should make it easier for people unfamiliar with the internals to focus
on the options relevant to them.

As a user of `deno_runtime` I feel like these should serve as good
defaults, getting people them started without having to tweak the
runtime. Additionally even if some changes are made, the usage of
`..Default::default()` will significantly help with code clarity and
verbosity.

runtime/worker.rs

@@ -18,6 +18,7 @@ use deno_core::serde_v8;
 use deno_core::v8;
 use deno_core::CompiledWasmModuleStore;
 use deno_core::Extension;
+use deno_core::FsModuleLoader;
 use deno_core::GetErrorClassFn;
 use deno_core::JsRuntime;
 use deno_core::LocalInspectorSession;
@@ -105,6 +106,41 @@ fn grab_cb(
   v8::Global::new(scope, cb)
 }
 
+impl Default for WorkerOptions {
+  fn default() -> Self {
+    Self {
+      web_worker_preload_module_cb: Arc::new(|_| {
+        unimplemented!("web workers are not supported")
+      }),
+      web_worker_pre_execute_module_cb: Arc::new(|_| {
+        unimplemented!("web workers are not supported")
+      }),
+      create_web_worker_cb: Arc::new(|_| {
+        unimplemented!("web workers are not supported")
+      }),
+      module_loader: Rc::new(FsModuleLoader),
+      seed: None,
+      unsafely_ignore_certificate_errors: Default::default(),
+      should_break_on_first_statement: Default::default(),
+      compiled_wasm_module_store: Default::default(),
+      shared_array_buffer_store: Default::default(),
+      maybe_inspector_server: Default::default(),
+      format_js_error_fn: Default::default(),
+      get_error_class_fn: Default::default(),
+      origin_storage_dir: Default::default(),
+      cache_storage_dir: Default::default(),
+      broadcast_channel: Default::default(),
+      source_map_getter: Default::default(),
+      root_cert_store: Default::default(),
+      npm_resolver: Default::default(),
+      blob_store: Default::default(),
+      extensions: Default::default(),
+      bootstrap: Default::default(),
+      stdio: Default::default(),
+    }
+  }
+}
+
 impl MainWorker {
   pub fn bootstrap_from_options(
     main_module: ModuleSpecifier,
@@ -533,7 +569,7 @@ mod tests {
       create_web_worker_cb: Arc::new(|_| unreachable!()),
       maybe_inspector_server: None,
       should_break_on_first_statement: false,
-      module_loader: Rc::new(deno_core::FsModuleLoader),
+      module_loader: Rc::new(FsModuleLoader),
       npm_resolver: None,
       get_error_class_fn: None,
       cache_storage_dir: None,

runtime/worker_bootstrap.rs

@@ -1,7 +1,12 @@
-use crate::ops::runtime::ppid;
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
 use deno_core::serde_json;
 use deno_core::serde_json::json;
 use deno_core::ModuleSpecifier;
+use std::thread;
+
+use crate::colors;
+use crate::ops::runtime::ppid;
 
 /// Common bootstrap options for MainWorker & WebWorker
 #[derive(Clone)]
@@ -24,6 +29,32 @@ pub struct BootstrapOptions {
   pub inspect: bool,
 }
 
+impl Default for BootstrapOptions {
+  fn default() -> Self {
+    let cpu_count = thread::available_parallelism()
+      .map(|p| p.get())
+      .unwrap_or(1);
+
+    let runtime_version = env!("CARGO_PKG_VERSION").into();
+    let user_agent = format!("Deno/{}", runtime_version);
+
+    Self {
+      runtime_version,
+      user_agent,
+      cpu_count,
+      no_color: !colors::use_color(),
+      is_tty: colors::is_tty(),
+      enable_testing_features: Default::default(),
+      debug_flag: Default::default(),
+      ts_version: Default::default(),
+      location: Default::default(),
+      unstable: Default::default(),
+      inspect: Default::default(),
+      args: Default::default(),
+    }
+  }
+}
+
 impl BootstrapOptions {
   pub fn as_json(&self) -> String {
     let payload = json!({