[DesignConsistency] Confusing message when adding a NuGet package

[karann-msft]

Messaging seems slightly confusing in this dialog. Title is "Preview" but the title in the dialog is "Review Changes" and the status shows "Installing". Output window got focus but nothing appeared there until OK was pressed.

It's unclear if anything has happened yet

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[karann-msft]

@rrelyea and I triaged this today.
Please do the following:

1. change the title of the dialog from "Preview" to "Preview Changes"
2. remove "Review Changes" and the space that it takes up :)