Add better breakpoint icons

[filipdutescu]

Description

Currently, breakpoints do not use a conventional symbol, such as the classic filled red circle, the empty circle or the circle with a warning sign.

Proposal

Use nerdfont icons to set more conventional icons for breakpoints (dependent on #2869).

UI mockup

[archseer]

I posted some comments on this here: #5952

[KenCox94]

@filipdutescu is this you delegating out from the original #5952 issue or just a place to move conversation from that original issues thread. I'm interested in this but new to contributing to helix. lmk

[filipdutescu]

@filipdutescu is this you delegating out from the original #5952 issue or just a place to move conversation from that original issues thread. I'm interested in this but new to contributing to helix. lmk

this is a way to independently track more advanced customisation of the original issue. this customisation is dependent on #2869, so in order to not bloc #5952, I opened this issue. This one is a continuation of the original, if it makes sense.