Autocompletion for filter text fields and text areas

[Bios-Marcel]

Todos:

• Preserve newlines when autocompleting
• Offer autocompletion directly after open paranthesis
• Offer autocompletion for binary operators (Could be difficult)
• Simplify usage of api
• Make sure popup doesn't render out of bounds
• Do a lookahead on completion to prevent accidentally recompleting an existing word partially
• Properly handle selection
• Use input.insert where possible instead of setText
• Make completion independent of content type to complete

  Currently it contains logic specific to the filter language

• Add indicator of whether the query is valid
• Fuzzy autocomplete Will be a separate issue after the PR

Imperfections I'll accept for now:

• Y out of bounds isn't treated
• Binary operators aren't autocompleted correctly.

  The completion is a hack implemented outside of the parser. We can only do full completion, not partial completion, due to the fact we don't run into the binaryExpression rule of the parser. I tried changing the parser, but to no success.

A solution to any parsing problems is potentially throwing away antlr and writing a custom parser.