Add anchors to link json artifact

[Mpdreamz]

Refactored LinkReference to use a dictionary for better anchor tracking and adjusted anchor validations. Added extensive test coverage, revamped test setup, and improved generator logic for markdown files.```

Several testing features are coming through in this PR too.

We can now bootstrap not just markdown fragments (Setup.Markdown) or full documents (Setup.Document) but also full virtual file system through Setup.Generate see:

static let generator = Setup.Generate [
    Index """
# A Document that lives at the root

*Welcome* to this documentation
"""
    Markdown "file.md" "*hello* world"
]

We can now also test different output markdown files explicitly

[<Fact>]
let ``validate file.md HTML`` () =
    generator |> converts "file.md" |> toHtml "<p><em>hello</em>world</p>"

We can now also do json diff testing similar to our html testing see #344 for more info about the better test failure messages.

[<Fact>]
let ``validate links.json`` () =
    generator |> convertsToJson ".artifacts/docs/html/links.json" jsonString

The text will be properly highlighted again:

Lastly but most importantly we now actually call DocumentationGenerator().GenerateAll() just like docs-builder does.

The output of which now flows properly to test output so we can see it in test explorers in any IDE:

[reakaleek]

🔥