process: allow StartExecution() to take a main script ID

The idea is to allow the C++ layer to run arbitrary scripts
as the main script. This paves the way for

- cctest of the execution of Node.js instances
- Earlier handling of per-process CLI options that affect
  execution modes (those usually do not make sense for the
  embedders).
- Targets like mkcodecache or mksnapshot.

Also moves the handling of `_third_party_main.js` into C++.

PR-URL: https://github.com/nodejs/node/pull/25474
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/node_native_module.h b/src/node_native_module.h
index 9a0afcc0b9..62c417a0b6 100644
--- a/src/node_native_module.h
+++ b/src/node_native_module.h
@@ -54,6 +54,8 @@ class NativeModuleLoader {
       std::vector<v8::Local<v8::Value>>* arguments,
       Environment* optional_env);
 
+  bool Exists(const char* id);
+
  private:
   static void GetCacheUsage(const v8::FunctionCallbackInfo<v8::Value>& args);
   // Passing ids of builtin module source code into JS land as