Option for pure-ESM mode

[rconnamacher]

Projects using native ECMAScript modules could use a command line flag to limit closure-calculate-chunks to only following ESM imports (import, import(), and export * from), and to ignore require(), goog.require(), and the like.

Code that uses the imperative RequireJS API for loading external libraries at runtime can cause tracebacks when closure-calculate-chunks attempts to parse them.

[ChadKillingsworth]

Do you have an example of the problematic code? The only goal of this project is to identify the correct source set and allocate the files to the correct output chuck for feeding into closure-compiler. If you have discoverable code that is not actually intended to be included in the compilation, there is not currently an option to exclude it.