[FEA] Support custom FileSystem that we could pack multiple js files.

[winterdl]

We could zip or using asar like, memory to pack multiple js files, when init the engine, we could using filesystem providers like:

Mercury(
....
   fileSystems: [
        MemoryFileSystem({
          "/test.js": """
          const md5 = require('md5');
          module.exports = md5('hello');
          """
        })
      ],
)