Log the `podcast_shared` event after the user actually shares the item

### Description

We currently log `podcast_shared` when the user selects an item type to share but before they actually share the item. We might want to only log this when the user actually shares the item. Additionally, this event logs a `action` property which indicates what type of sharing occurred. We could log a similar property with the `UIActivity.ActivityType` to indicate some common ones such as links or messages.

### Step-by-step reproduction instructions

Enable the `tracksLogging` feature flag

1. Navigate to an Episode Detail page
2. Tap the Share button in the upper right
3. Select an option to share
4. Notice that the `podcast_shared` event is logged

### Screenshots or screen recording

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### Did you search for existing bug reports?

- [X] I have searched for existing bug reports.

### Device, Operating system, and Pocket Casts app version

_No response_

Start by tracing the share flow from the Episode Detail page with the tracksLogging flag enabled, following the Share button through item selection and the system share action. Done means podcast_shared is logged only after the item is actually shared, with a property identifying the relevant UIActivity.ActivityType for common sharing methods.

Written by the indexing model from the issue text.