Update API doc generation and mdoc conversion to use net8.0

[pjcollins]

Context: #7958 (comment)

We should update our targets and pipelines related to API doc generation to use .NET instead of mono.

[jpobst]

Note that there are 2 parts here:

1. Generate the XML documentation from the net8.0-android33.0 Mono.Android.dll instead of the monoandroid10 Mono.Android.dll.
2. Use .NET instead of Mono to run tools such as MDoc.

(1) is blocking us from removing monoandroid10 Mono.Android.dll so it is the more immediate concern.

However, it may make sense to do both parts at the same time. 🤷‍♂️

[pjcollins]

Part 1 should be fixed by #8007. We can look at updating to a version of mdoc that supports net6.0 (mono/api-doc-tools#639) in a future PR.

[pjcollins]

Part 2 is hitting an issue during the update that requires further investigation:

     Updating: Android.Icu.Lang.UCharacter
     mdoc: Mono.Documentation.MDocAssemblyException: Error processing Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065 from obj/docs-gen-temp/xamarin-android-sdk-13/Mono.Android.dll
      ---> System.ArgumentException: The surrogate pair (0xDBFF, 0x3B) is invalid. A high surrogate character (0xD800 - 0xDBFF) must always be paired with a low surrogate character (0xDC00 - 0xDFFF).
        at System.Xml.XmlTextEncoder.WriteSurrogateChar(Char lowChar, Char highChar)
        at System.Xml.XmlTextEncoder.Write(String text)
        at System.Xml.XmlTextWriter.WriteString(String text)
        at System.Xml.XmlAttribute.WriteContentTo(XmlWriter w)
        at System.Xml.XmlAttribute.WriteTo(XmlWriter w)
        at System.Xml.XmlElement.WriteStartElement(XmlWriter w)
        at System.Xml.XmlElement.WriteElementTo(XmlWriter writer, XmlElement el)
        at Mono.Documentation.MDocUpdater.WriteXml(XmlElement element, TextWriter output) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 584
        at Mono.Documentation.MDocUpdater.<>c__DisplayClass75_0.<WriteFile>b__0(String file) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 593
        at Mono.Documentation.MdocFile.UpdateFile(String file, Action`1 creator) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MdocFile.cs:line 63
        at Mono.Documentation.MDocUpdater.DoUpdateType2(String message, XmlDocument basefile, TypeDefinition type, FrameworkTypeEntry typeEntry, String output, Boolean insertSince) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 1824
        at Mono.Documentation.MDocUpdater.DoUpdateType(AssemblySet set, AssemblyDefinition assembly, TypeDefinition type, FrameworkTypeEntry typeEntry, String basepath, String dest) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 922
        at Mono.Documentation.MDocUpdater.DoUpdateAssembly(AssemblySet assemblySet, AssemblyDefinition assembly, XmlElement index_types, String source, String dest, HashSet`1 goodfiles) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 1135
        at Mono.Documentation.MDocUpdater.DoUpdateAssemblies(String source, String dest) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 1078
        --- End of inner exception stack trace ---
        at Mono.Documentation.MDocUpdater.DoUpdateAssemblies(String source, String dest) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 1085
        at Mono.Documentation.MDocUpdater.Run(IEnumerable`1 args) in /Users/runner/work/1/s/mdoc/Mono.Documentation/MDocUpdater.cs:line 467
        at Mono.Documentation.MDoc.Run(String[] args) in /Users/runner/work/1/s/mdoc/Mono.Documentation/mdoc.cs:line 82
        at Mono.Documentation.MDoc.Main(String[] args) in /Users/runner/work/1/s/mdoc/Mono.Documentation/mdoc.cs:line 20

[dotnet-policy-service]

Hi @pjcollins. We have added the "need-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[pjcollins]

Seems like this is working for us now.