Forecast charts announce "Empty group"

[partly-igor]

Description

When a user using a screen reader navigates to the charts view in a forecast-item and moves focus to a chart, the screenreader announces "empty group" (when tested using VO). We currently don't have an aria-role or text alternative within the canvas element, and the table that contains the text data is hidden, so screenreader users are not able to get any information from the chart.

As discussed with @eric-gade possible solutions include:

• Refer to table rows by aria-labelledby
• Refer to the whole table by aria-labelledby
• Custom SR only explaining that they should switch to table view

Acceptance criteria

• Navigating to a chart a screen reader user is able to get meanigful information - either the data or a direction to the table containing the data.