include es5 versions of individual source files in build

[amagee]

This pull request is basically a working proof of concept of this comment: #725 (comment)

I haven't thought through all the issues but hopefully this can get a discussion going.

[mcwhittemore]

@amagee - Thanks for pushing forward for this via a PR. My main concern for a PR that changes the build system is ensuring that the result is non-breaking for other users (we've failed at this in the past). How would your propose testing this to make sure it works in many situations?

[amagee]

Yep good question.

1. People using the published npm packages
   Assuming you run npm run build as part of your scripts to publish to npm, and the build succeeds, it should not be possible for this to break anything for anyone, since the main file generated by the build is unchanged; there are just new additional files. People who just import Mapbox Draw normally should be unaffected by the new files.

2. People running builds themselves
   In its current form this could cause issues (eg. if run on a system that doesn't have sed, eg. Windows). This should be easily fixable though, if it's decided this is a sensible approach then I could replace the shell script with a Javascript file that does the same thing.

[jmking]

Wondering if there is any more feedback on how we might proceed with this? (I work with @amagee)

[kkaefer]

Superseded by #945