Added safe-area handling to BottomBannerViewController.

[JThramer]

Fixes #1978. Adds a "padding" view that accounts for the device's bottom safe area, if any.

Test reference:

To-do:

• Add Snapshot Test
• Changelog entry.

/cc @mapbox/navigation-ios

[frederoni]

An additional view to add some padding seems excessive. Can we constrain the bottom element in the bottom banner with safeBottomAnchor?

Also, the NightStyle inherits from the DayStyle, so we need an appropriate color there as well. Can the padding view’s background color be transparent? Much like the UIStackView, a padding view should be a non-rendering view. However, preferably, we shouldn't have a padding view at all.

[JThramer]

Posterity: after talking with @frederoni, we decided to make the bottom padding area a BottomBannerView type. That way, the padding area can stay consistent with the banner, and we won't have to add extra stuff to the style.

We chatted about this, compromised on one type for both views (banner and padding)