Godot: Add a multi-line text editor for exported strings

[MightyPrinny]

Godot version:
3.1 beta 4

Issue description:
Editing exported strings is very uncomfortable when you want to use them as multi-line text because new lines can only be added by copying text from an external text editor.

My suggestion is to add a button to the right side of the line edit that opens a window where you can edit mult-line text.

[akien-mga]

You can already use export(String, MULTILINE) var text for that, see https://docs.godotengine.org/en/latest/getting_started/scripting/gdscript/gdscript_basics.html#exports

[MightyPrinny]

You can already use export(String, MULTILINE) var text for that, see https://docs.godotengine.org/en/latest/getting_started/scripting/gdscript/gdscript_basics.html#exports

Is this possible in C#? this is not mentioned in https://docs.godotengine.org/en/latest/getting_started/scripting/c_sharp/c_sharp_differences.html#other-differences

[somnivore]

[Export(PropertyHint.MultilineText)] should be the C# variation

[akien-mga]

It would be good to enhance the C# docs linked accordingly, it's quite terse currently on how options are available for [Export].

[MightyPrinny]

[Export(PropertyHint.MultilineText)] should be the C# variation

Thank you so much.