[dynamic_color] Impl. [isCorePaletteSupported] API #390

[alexrintt]

Description

I did need a built-in method to verify if [getCorePalette] is supported by the host platform without third-party solutions such as pub.dev/available or pub.dev/device_info_plus,
see also #390.

Note: this PR includes only the [isCorePaletteSupported] API, I'll try to send another PR to implement [isAccentColorPaletteSupported] also, if/when it gets approved.

Tests

• Added test cases to check whether or not the method is handling null, false and true values coming from the host platform using the same way it's currently implemented for the other APIs.

Issues

Partially fixes #390 since this PR is missing the [isAccentColorPaletteSupported] which is just the same check as I did in this PR but for the desktop platforms.

Checklist

• I've reviewed the contribution guide.
• I've updated the package CHANGELOG.md

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[guidezpl]

Thanks for this. However I think it would be preferable to add this check as a short-circuit exit to the existing API (getCorePalette), rather than to add a new method. LMK if you'd like to do this

[alexrintt]

Sure, since we are going to return null when the dynamic color features aren't available this PR doesn't make sense because the plugin is already returning null when the SDK Int is below S.

---

Also, since for Android there are a few more checks to do in order to determine if this API is available or not, I am planning to open another PR to add these checks in this plugin as well.

In order to do so I was going to add a dependency to com.google.android.material:material and replace Build.VERSION.SDK_INT >= Build.VERSION_CODES.S with DynamicColors.isDynamicColorAvailable() at the getCorePalette verification.

Does that sound reasonable?

[guidezpl]

Sounds reasonable!