Use ES module for the web worker in playground

[adelhult]

Describe the bug
To support all major browser the web worker used to run the compiler in the playground currently uses a bit of an ugly import system. This is because ES modules (i.e. js that uses the nice import syntax) is not supported inside of web workers in Firefox. It looks like this is about to change in the next upcoming version, so we should switch to the cleaner solution then.

[CMDJojo]

Current state: See pr #154. Firefox 111 has support for module workers but it is controlled by a flag which is disabled by default. It would probably be too much of an inconvenience for users to have to enable a flag to use our playground on a major browser, so I think we should shelve this until it has support without using a custom flag.