How to Format Bar Labels to Add a $ Symbol or Custom Text in Victory Native

### Description

I’m using Victory Native for creating bar charts, and I need to format the labels on the bars so that I can either:

1. Add a $ symbol before the amount displayed on each bar.
2. Pass custom text to be displayed on top of the bars instead of the default labels.

Start by locating the Victory Native bar-chart label rendering and formatting entry point, then check how the current default labels are produced. The work is done when bar labels can show a dollar prefix or caller-supplied custom text, with the displayed result matching the requested examples.

Written by the indexing model from the issue text.