Properly address property pages item ordering

[MiYanni]

Related: #6989

Currently, CPS does not seem to maintain item ordering. This can be seen in the Target Framework dropdown. For now, we are putting in a hotfix to manually order these items. However, the proper fix has a couple options:

1. Investigate and fix CPS item ordering preservation
   a. For target framework, the items are declared here and this ordering should be preserved: https://github.com/dotnet/sdk/blob/master/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.SupportedTargetFrameworks.props
2. Add functionality to the Rule definitions as to allow custom ordering.

These two options could both be completed, where the default is preserved ordering and it is optional to add your own ordering to the Rule definitions. When this PR is completed, please revert the hotfix here:

[tmeschter]

A third option would be to update Microsoft.NET.SupportedTargetFrameworks.props to include explicit ordering information separate from the order of items in the .props.

[tmeschter]

Fourth option: parse the Include for each item from that .props (e.g. .NETCoreApp,Version=v2.1) to group items by the framework family (e.g. .NETCoreApp) and then order by version number within that family.

[drewnoakes]

I would vote for adding specific DisplayOrder metadata to the items returned by the SDK.

[melytc]

Fourth option: parse the Include for each item from that .props (e.g. .NETCoreApp,Version=v2.1) to group items by the framework family (e.g. .NETCoreApp) and then order by version number within that family.

To avoid parsing, this is "already done" in the SDK side: instead of capturing all of the values in SupportedTargetFramework item, we could store and use each framework's ItemGroup Microsoft.NET.SupportedTargetFrameworks.props.

[drewnoakes]

CPS now has a way for us to obtain the original item ordering, which may fix this.

We'll need code such as:

var after = projectChangeDescription.After.Items as IDataWithOriginalSource<KeyValuePair<string, IImmutableDictionary<string, string>>>;

This gives an ICollection<KeyValuePair<string, IImmutableDictionary<string, string>>> which has the original MSBuild order.

There are three places we could do this in the current code. Search for https://github.com/dotnet/project-system/issues/7025 to find them.

[drewnoakes]

There's a cut of this in the fix-7025-item-ordering branch on my fork. It's blocked on needing the IDataWithOriginalSource<> interface on evaluation data, not just build data. I've asked CPS the feasibility of adding this support in ProjectEvaluationSubscriptionService.

[drewnoakes]

Evaluation data is handled differently to build data, and there's more re-use of the underlying immutable data structures over time. This means there's less likelihood we'd get ordered evaluation data using IDataWithOriginalSource<>. The approach should be fine for build data though.