Support Legend Text Styling (To Visualize Hover)

### Feature Proposal

## Proposal

I propose to to add a new `fontStyle` property (or something similar) to the [LegendItem interface](https://www.chartjs.org/docs/latest/api/interfaces/LegendItem.html).

This should allow at least the following values:
- 'normal' (DEFAULT)
- 'bold'
- 'underlined'

## Use Case

We use an on click handler to hide datasets using the legend. This is currently a 'hidden feature' as there is no visual clue to the user that the legend is an interactive user element. You have to know it or read the documentation.

To increase accessibility, we would like to change the text style of the currently hovered element to 'bold' or 'underlined'.

## Side Note

This could be a general pattern to implement for other labels in ChartJS.

### Possible Implementation

_No response_