Podcast Player Block: Enable expandable episode descriptions instead of simply truncating descriptions

### Is your feature request related to a problem? Please describe.

This feature request was suggested by a customer in live chat today. The issue that the customer identified is that podcast episode descriptions, particularly for the episode being played, is truncated at a predefined length, and there is no option to expand the description to read the whole description.

Instead, the episode description ends with `...`, like this:

### Describe the solution you'd like

Our customer suggested that the truncated text expand when a site visitor taps on the text, or otherwise triggers some sort of expansion option (perhaps an icon, or "Read more" link/button).

### Describe alternatives you've considered

In the context of mobile devices, the customer suggested the following possible alternatives:

>along the same lines i was wondering if i could adjust the text scaling for the names in the same podcast block in the mobile client the names of each episode takes alot of screen space so i was considering reducing the text size when users are on a mobile #platform

### Additional context

This suggestion was made in 27171967-hc with a follow-up in 3691353-zen.

Locate the Podcast Player Block implementation and reproduce the current description truncation, including the playing episode and mobile layout. Read the existing block UI and related tests, if present, then define the interaction and responsive behavior before implementing it; done means visitors can reveal the full description without disrupting playback.

Written by the indexing model from the issue text.