chore: allow the node entrypoint to be a builtin module

This floats two patches onto the node 12 branch that I don't think we can upstream.

#### `run_main_module.js`

The default behavior of node is to `path.resolve(firstArg)` to figure out what JS file to load.  Issue here is that we use that for `browser/init.js` which now doesn't exist on disk.  This adds an exception that won't affect user code to allow node to boot-up internal modules (in this case anything in the `electron/js2c` scope.

#### `loader.js`

Similar to the above, the loader uses `process.argv[1]` to figure out when to break for `--inspect-brk` this updates the logic to use an Electron provided `process._firstFileName`

lib/internal/main/run_main_module.js

@@ -5,8 +5,11 @@ const {
 } = require('internal/bootstrap/pre_execution');
 
 // Expand process.argv[1] into a full path.
+// Allow direct module name loads if it is a built-in electron module
+if (!process.argv[1] || !process.argv[1].startsWith('electron/js2c')) {
 const path = require('path');
 process.argv[1] = path.resolve(process.argv[1]);
+}
 
 prepareMainThreadExecution();
 

lib/internal/modules/cjs/loader.js

@@ -781,6 +781,13 @@ Module.prototype._compile = function(content, filename) {
   if (process._breakFirstLine && process._eval == null) {
     if (!resolvedArgv) {
       // We enter the repl if we're not given a filename argument.
+      // process._firstFileName is used by Embedders to tell node what
+      // the first "real" file is when they use themselves as the entry
+      // point
+      if (process._firstFileName) {
+        resolvedArgv = process._firstFileName
+        delete process._firstFileName
+      } else
       if (process.argv[1]) {
         resolvedArgv = Module._resolveFilename(process.argv[1], null, false);
       } else {