Add new constructor to AvaloniaDictionary and include unit tests #17311

[IoannTerrible]

#17311

What does the pull request do?

This pull request adds a new constructor to AvaloniaDictionary<TKey, TValue> that accepts an existing Dictionary<TKey, TValue>. The goal is to provide an easier and more efficient way to initialize AvaloniaDictionary with pre-existing dictionary data.

What is the current behavior?

Currently, AvaloniaDictionary lacks a constructor that directly accepts a Dictionary<TKey, TValue>. Developers have to manually copy elements into AvaloniaDictionary, which increases boilerplate code and is less efficient.

What is the updated/expected behavior with this PR?

With this PR, developers can initialize AvaloniaDictionary with an existing dictionary directly, simplifying the code and reducing manual effort.
To test:

• You can create an AvaloniaDictionary by passing a populated dictionary and verify that all entries are correctly initialized.
• Passing null should throw an ArgumentNullException.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

No breaking changes are introduced, as this PR simply adds an overload to the existing constructors.

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052726-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[IoannTerrible]

@cla-avalonia agree

[robloo]

Should the new constructor be an IDictionary interface rather than concrete class?

[maxkatz6]

This ctor overload seems to be the most complete:
https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.-ctor?view=net-8.0#system-collections-generic-dictionary-2-ctor(system-collections-generic-ienumerable((system-collections-generic-keyvaluepair((-0-1))))-system-collections-generic-iequalitycomparer((-0)))