[Tooling] Improve imports in antlr-worker.js

[pcnfernando]

Description:
At the moment we have imports defined in antlr-worker.js which will be imported for each initialization of antlr-worker which will be called for opening of each tab.
https://github.com/siddhi-io/distribution/blob/master/tooling/components/io.siddhi.distribution.editor.core/src/main/resources/web/editor/js/source-editor/antlr-worker.js#L16

This in-turn causes app validation to delay until these scripts are downloaded.

We can improve it to import needed scripts as in https://github.com/siddhi-io/distribution/blob/master/tooling/components/io.siddhi.distribution.editor.core/src/main/resources/web/editor/js/source-editor/editor.js#L8