Code Quality: Fix CA1859 and CA1829

[gumbarros]

Description

.NET 8 introduce this 2 new analyzers to improve performance

https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1829
https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1859

Concerned code

CA1829:

Files/src/Files.App/Services/JumpListService.cs

Line 165 in 27ef249

var pinnedItemsCount = instance.Items.Where(x => x.GroupName == JumpListPinnedGroupHeader).Count();

CA1859:

Files/src/Files.App/Data/Commands/Manager/ModifiableCommandManager.cs

Line 28 in 27ef249

private static IDictionary<CommandCodes, IRichCommand> CreateModifiableCommands() => new Dictionary<CommandCodes, IRichCommand>

Gains

• Better readibility (no useless casting at CA1859 )
• Better performance

Requirements

• Refactor to the suggestions of the analyzer

Comments

I created #14951 but it was recused, it has compile errors and do more things, if authorized I can create a new PR

[yaira2]

@d2dyno1 @0x5bfa

[0x5bfa]

Sounds good. I was going to do that so it's already ready to build.