Improve Gatling's scripts auto-completion

[geraldpereira]

Add auto-completion for :

• asJson
• headers
• Http Proxy configuration
• SSE
• WebSockets
• JMS

Use a Scala parser?

• https://tomassetti.me/parsing-in-javascript/#tools
• https://github.com/tunnelvisionlabs/antlr4ts
• https://github.com/antlr/grammars-v4/blob/master/scala/Scala.g4
  Does not work in the web browser: TypeError: Class constructor Lexer cannot be invoked without 'new' tunnelvisionlabs/antlr4ts#326

Use JS version instead?
https://github.com/antlr/antlr4/blob/master/doc/javascript-target.md

Install Antlr locally https://www.antlr.org/download.html
Generate the parser java -Xmx500M -cp antlr-4.7.2-complete.jar org.antlr.v4.Tool -Dlanguage=JavaScript Scala.g4
Use the genrated code
https://stackoverflow.com/questions/40463441/typescript-how-to-import-a-class-from-a-javascript-fil

[geraldpereira]

Must also set the embedded documentation to the proper cheat sheet entry when an autocomplete is done.