Move to the paged document support in Verify 33.3

[SimonCropp]

Moves Verify.PDFium onto the source and derived targets that Verify 33.3 added for paged documents (Verify#1951), and takes the package from 1.5.0 to 2.0.0.

The converter now says which of its targets is the document and which were computed from it. Verify compares the document first, so a file derived from it is only given the benefit of its comparer while the document itself is unchanged, and DiffEngine's viewer shows the files derived from a document beneath it and accepts them with it.

It is a major version because what an existing test suite has to change is listed below. Verify and its adapter are pinned at 33.3.0.

Migrating from 1.x

Version 2 moves to the paged document support in Verify 33.3. The file names are unchanged. What differs:

1.x	2.x
Initialize(outputs: PdfiumOutputs.Png)	VerifierSettings.PageText(PageTextPlacement.None)
Initialize(outputs: PdfiumOutputs.Text)	VerifierSettings.ExcludeDerivedTargets("png")
Initialize(outputs: PdfiumOutputs.None)	Both of the above
.ExcludePdfDocument()	.ExcludeTargets("pdf")

The info file has the shape every paged document has: the document properties under Document, and each page as its Number, its size under Info, and its Text.

{
  PageCount: 1,                      {
  Properties: {                        Document: {
    Producer: PDFsharp 6.2.4             Producer: PDFsharp 6.2.4
  },                                   },
  Pages: [                             PageCount: 1,
    {                                  Pages: [
      Width: 612.0,                      {
      Height: 792.0,                       Number: 1,
      Text: Hello, World!                  Info: {
    }                                        Width: 612.0,
  ]                                          Height: 792.0
}                                          },
                                           Text: Hello, World!
                                         }
                                       ]
                                     }

So every .verified.txt changes once, and nothing else does.

Testing

Built in Release and run with the commands CI uses, against Verify 33.3.0 from nuget.org: 22 passed.