Disable font ligatures for lookahead/lookbehind prefixes (regex)

[andrebrait]

While this was a recent development in Fira Code, I think it's something they did right and maybe should also be implemented here (all screenshots are from JetBrains Mono 1.0.2).

• FiraCode in IntelliJ IDEA in a Java file:
  

• JetBrains Mono in IntelliJ IDEA in a Java file:
  

• FiraCode in IntelliJ IDEA in a Python file:
  

• JetBrains Mono in IntelliJ IDEA in a Python file:
  

Sometimes, the ligature used is different depending on the text editor, too:

• FiraCode in Visual Studio Code in a Plain Text file (identical results in a Shell Script file):
  

• JetBrains Mono in Visual Studio Code in a Plain Text file (identical results in a Shell Script file):
  

Other times, both end up using ligatures, though different ones, depending on the text editor, too (and maybe this is an issue with IntelliJ?):

• FiraCode in IntelliJ IDEA in a Shell Script file:
  

• JetBrains Mono in IntelliJ IDEA in a Shell Script file:
  

See tonsky/FiraCode#578 for more details on what Fira Code did in this case.

From their changelog:

Disabled ligatures after regexp lookahead/lookbehinds (?<=< (?<=> (?<==> (?<=| (?<== (?=:= (?=!= (?== (?=== (?==> (?=> (?=>> (?=<< (?=/= (?!! (?!!. (?!= (?!== (?<!! (?<!!. (?<!= (?<!== (?<!--

[philippnurullin]

@andrebrait Looks interesting! Thanks, we will include it in future updates.