Declare const in doalogue

[Supamiu]

Is your feature request related to a problem? Please describe.
When writing dialogues that reuse the same value in various places (for instance, an id of something), having to copy it everywhere creates bad maintenance issues. Having to create a global for each case of this is also not a good option regarding maintenance.

Describe the solution you'd like
A syntax like const MY_CONST = "my_something" for instance that would create a reusable declaration accross the file.

Describe alternatives you've considered
For now I'm just doing copy and paste of the said ID when needed.

Additional context
My use case is that we have a dialogue that can trigger a given quest in many ways, using its uuid, which is copied in way too many places for this dialogue

[nathanhoad]

I'll have a look at implementing this when I get a chance.

[nathanhoad]

I finished implementing this but I'm not overly a fan of the complexity it introduces for something that can already be achieved with a constant in regular state. For that reason I'm going to close the issue for now (but I've kept the local branch just in case).