Avoid unnecessarily resizing dictionary while calculating project closure

[kartheekp-ms]

Thanks to @davkean for identifying a performance improvement in NuGet.

ToDictionary does not let you specify an underlying starting capacity. This causes it to inherit the default size and unnecessarily resize itself multiple times in a large solution. Added a version of ToDictionary that lets you specify a default.

https://github.com/davkean/NuGet.Client/blob/e97d556a83750bb4f8017e3640bc699d04832657/src/NuGet.Core/NuGet.ProjectModel/DependencyGraphSpec.cs#L191-L192

This was allocating 0.5% (150 MB) opening a 1000 project solution.

NuGet/NuGet.Client#4129 (comment)

[aortiz-msft]

@kartheekp-ms - Could you please help understand what is the improvement for OrchardCore?

[aortiz-msft]

@jebriede so that this can be tracked with the others