[Tizen] Adds the Unified Theme Manager

[rookiejava]

Description of Change

This PR adds a theme manager to efficiently and consistently manage values (parts, styles, etc.) that are dependent on the platform theme file from various profiles (Phone, TV, Watch, and so on) and Tizen products.

The constant values provided from the platform theme file (*.edc) are unified and managed through the ThemeConstants class. The ThemeConstants is composed of Style, Part, Signal, Resource, and ColorClass for each widget, and each item is also subdivided according to TargetIdiom.

ThemeManager is also newly added to make the each renderer implementation simpler and more intuitive. Instead of inconsistently hard-coded values in each renderer, you can use convenient and abstract utility methods provided by ThemeManager.

Issues Resolved

None

API Changes

namespace Xamarin.Forms.Platform.Tizen
Added:

• class ThemeConstants
• class ThemeManager
• class FormsLayout and it's subclasses

namespace Xamarin.Forms.Platform.Tizen
Added:

• class FormsWatchLayout and it's subclasses

Platforms Affected

-Tizen

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[rookiejava]

@samhouts Can you cherry-pick this change to 4.8.0 branch? Upcoming PRs (including #11820) are dependent on this change, so it would be nice if it was applied in 4.8.0. (If not, we'll submit them all to the 5.0 branch.)

[samhouts]

@rookiejava We're hoping to limit 4.8.0 to just regressions at this point, but I'm happy to make exceptions for you! It looks like #11820 is on 5.0.0, FYI, if you need that one retargeted. Thanks!