Highlighting of multi-line `if` fields

**Is your feature request related to a problem? Please describe.**
I often use a complex `if` field to enable smart skipping of the `push` event trigger.
(note that without the `${{ }}` the editor yields a syntax error saying `Unexpected symbol: '=='`. Adding a space after the initial `!` seems to eliminate the error, but I'm not sure if that works (#290).)

Writing it like that looks horrible so I format it as a multi-line string, but then the syntax highlighting is broken.

**Describe the solution you'd like**
It would be really nice to have syntax highlighting for multi-line expressions. It would look something like this: