Use collection initializers or expressions

[kzu]

This is the recommented way and is starting to be applied throughout the dotnet runtime. See https://github.com/dotnet/runtime/pull/105122.

Applied code fixes for:

• IDE0028: https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0028?pivots=dotnet-8-0
• IDE00300: https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0300

Microsoft Reviewers: Open in CodeFlow

[kzu]

The second commit catches the cases of new[] { that were not flagged (nor autofixed) by the analyzers.

The ambiguous API call compilation errors are due to not having the .NET 9 compiler smarts :(