Modernize folderdialog

[clairernovotny]

This PR fixes #1 by implementing a Vista-style folder dialog.

Current dialog:

With this PR, the Vista-style dialog:

[merriemcgaw]

Can we see some Unit Tests with this PR? @AdamYoblick and @zsd4yr have some examples elswhere in WinForms.

[clairernovotny]

@merriemcgaw I would love to have some unit tests for this, but it was unclear how that can be accomplished. I was waiting for an example or the scaffolding of a unit test project to be available.

Also, I thought the tests @AdamYoblick were pretty basic and not UI tests. The Dialog blocks the calling thread and needs UI automation to manipulate it. I fully agree on the need for tests, just had not seen any infrastructure for adding one in yet.

[clairernovotny]

I can certainly add something to https://github.com/dotnet/winforms/tree/master/src/System.Windows.Forms/tests/functests if the p2p ref works now; I know that was being looked into before.

[merriemcgaw]

@onovotny Could you possibly provide before and after screenshots of the Folder dialog.

[clairernovotny]

@merriemcgaw Done

[shanselman]

[LanceMcCarthy]

This was an epic PR

[daniel-white]

Awesome to see this sort of transparency w/ Windows Forms!

[mattiascibien]

Been waiting for this since Windows Vista 👍

[orange-pig]

Epic update

[samuelGrahame]

This is amazing

[KevinAdams05]

Was the icon updated? The screenshot shows that it has the default form icon.

[samuelGrahame]

Was the icon updated? The screenshot shows that it has the default form icon.

maybe it gets it from the running program, but good point.

[RussKie]

docs - dotnet/docs#14153