Update `Module_With_Tag` and `Module_Tag`

## Feature Description

Update `Module_With_Tag` to include `get_tag()` method which returns `Module_Tag` instance.

Update `Module_Tag` to have `get_comment_text_before` and `get_comment_text_before` methods for returning translatable string placed in comment above module tag. For more info check this [comment](https://github.com/google/site-kit-wp/pull/8098#discussion_r1459435627)

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## Acceptance criteria

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## Implementation Brief

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### Test Coverage

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## QA Brief

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## Changelog entry

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