Add xml attribute to optimize importing of classes on Forms

[martijn00]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Feature

⤵️ What is the current behavior?

🆕 What is the new behavior (if this is a feature change)?

💥 Does this PR introduce a breaking change?

No

🐛 Recommendations for testing

📝 Links to relevant issues/docs

🤔 Checklist before submitting

• All projects build
• Follows style guide lines (code style guide)
• Relevant documentation was updated (docs style guide)
• Rebased onto current develop

[Cheesebaron]

Hmm the build doesn't like this:

AssemblyInfo.cs(7,12): error CS0246: The type or namespace name 'AssemblyVersionAttribute' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]
AssemblyInfo.cs(7,12): error CS0246: The type or namespace name 'AssemblyVersion' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]
AssemblyInfo.cs(8,12): error CS0246: The type or namespace name 'AssemblyFileVersionAttribute' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]
AssemblyInfo.cs(8,12): error CS0246: The type or namespace name 'AssemblyFileVersion' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]
AssemblyInfo.cs(9,12): error CS0246: The type or namespace name 'AssemblyInformationalVersionAttribute' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]
AssemblyInfo.cs(9,12): error CS0246: The type or namespace name 'AssemblyInformationalVersion' could not be found (are you missing a using directive or an assembly reference?) [C:\projects\mvvmcross\MvvmCross.Forms\MvvmCross.Forms.csproj]