[Analytics Hub] Extract DeltaPercentage entity

[rachelmcr]

Closes: #8243
⚠️ Depends on #8317 ⚠️

Description

This extracts DeltaPercentage from the StatsDataTextFormatter, for use as a separate entity.

The original idea behind DeltaPercentage was to just be a representation of the formatted string/direction in StatsDataTextFormatter. Given that so many report card values depend on the DeltaPercentage, it seems relevant as a separate entity. This will help simplify the view model setup for each analytics card in the Analytics Hub.

Changes

• Extracts DeltaPercentage from the StatsDataTextFormatter. For the sake of formatting the delta percentage string, we still use StatsDataTextFormatter to generate the delta from the order stats data.
• Updates the analytics card view models to accept a DeltaPercentage. The convenience inits for each analytics card now maps the delta in the view model to the respective properties on the card.

Testing

There should be no change in behavior:

1. Launch the app.
2. Tap "See more" on the My Store dashboard.
3. Confirm the Analytics Hub loads with the expected delta strings, colors, and charts.

Submitter Checklist

Update release notes:

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr8320-9e8f0ad on your iPhone

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[ealeksandrov]

Great work, viewmodels seem much more readable now!