[SIW-1978] Fix a11y issues of list item header and action element

[gispada]

Short description

This PR modifies the accessibility props of ListItemHeader to fix how the header is announced. To be more specific:

• The header label is announced independently as a header;
• The optional action item on the right is announced with its own accessibility label, without the header label.

List of changes proposed in this pull request

• Made the header view accessible with role header
• Removed accessibility from the outer component view
• Removed concatenation of header label and action label

How to test

Use a screen reader to announce the list item header, with and without the end element. Ensure each part is announced correctly, in the right order.

[dmnplb]

@gispada Have you already tested the accessibility on both iOS and Android? If so, have you tested on a real physical device or a virtual one?

[gispada]

I tested on both platforms on a real device.