Allow closure_js_binary user to control --module_resolution flag

Currently this is hard-coded to BROWSER:
https://github.com/bazelbuild/rules_closure/blob/4c559574447f90751f05155faba4f3344668f666/java/com/google/javascript/jscomp/JsCompilerRunner.java#L64

That causes an error with ES2015 import syntax:
```
ERROR: /usr/local/google/home/alexeagle/Projects/rules_typescript/examples/es6_output/BUILD.bazel:38:1: Compiling 3 JavaScript files to examples/es6_output/closure.js failed: Worker process sent response with exit code: 1.
ERROR - Failed to load module "./greeter"
Codes: JSC_JS_MODULE_LOAD_WARNING

1 error(s), 0 warning(s)
```

/cc @achew22

Start with java/com/google/javascript/jscomp/JsCompilerRunner.java at the linked module-resolution setting, then trace how closure_js_binary supplies compiler options. Use the examples/es6_output/BUILD.bazel case as validation; done means users can control --module_resolution instead of always using BROWSER and ES2015 imports compile successfully.

Written by the indexing model from the issue text.