[generator] Add --doc-comment-verbosity=intellisense+extraremarks

[jonpryor]

Context: dotnet/android@a7413a2
Context: https://github.com/xamarin/android-api-docs
Context: https://github.com/xamarin/android-api-docs/blob/035344f961fd391bcad9715ea690afa3b88d6142/docs/Mono.Android/en/Java.Lang/Object.xml#L34-L41

dotnet/android@a7413a23 asked:

What do we want? Updated documentation!

About that…

Our existing documentation at xamarin/android-api-docs includes
a copyright notice for every member, e.g.

<remarks>
  <para>
    <format type="text/html">
      <a href="https://developer.android.com/reference/java/lang/Object" title="Reference documentation">Android platform documentation</a>
    </format>
  </para>
  <para>Portions of this page are modifications based on work created and shared by the <format type="text/html"><a href="https://developers.google.com/terms/site-policies" title="Android Open Source Project">Android Open Source Project</a></format> and used according to terms described in the <format type="text/html"><a href="https://creativecommons.org/licenses/by/2.5/" title="Creative Commons 2.5 Attribution License">Creative Commons 2.5 Attribution License.</a></format></para>
</remarks>

The need to provide this copyright notice is why 7574f16 added the
java-source-utils.jar --doc-* options, so that the above notice
could be appropriate inserted.

The problem is that generator only emits the copyright notice when
generator --doc-comment-verbosity=full is used, and "full" output
is incomplete (many constructs aren't supported) and buggy (many
constructs result in "invalid" member references which may cause
breakage with mdoc update ¹).

Square this circle by adding a new
generator --doc-comment-verbosity=intellisense+extraremarks value,
which emits "intellisense" plus the "extra remarks" output, which
includes the copyright notice and documentation links.

This allows us to have the benefits of intellisense (faster,
semantically correct output) and also retain the extras.

Footnotes

1. mdoc update for "full" output will eventually fail with:

     System.Xml.XPath.XPathException: 'altmember[@cref='!:Java.Interop.Tools.JavaSource.SourceJavadocToXmldocGrammar+<ToXmlContent>d__9 and
     <c>
       <see cref="#EXTRA_EMBEDDED_SUBSCRIPTION_SMDX_REASON_CODE" />
     </c>
   
     In the case where ErrorCode contains a value of 0, it means it's an unknown error. E.g Intent
     only contains <c>
       <see cref="#OPERATION_DOWNLOAD" />
     </c> and ErrorCode is 0 implies this is an unknown
     Download error.']' has an invalid token.
       at MS.Internal.Xml.XPath.XPathParser.CheckToken (MS.Internal.Xml.XPath.XPathScanner+LexKind t) [0x00023] in <6062976fd2cb473f91f94556758db404>:0
     …
   

   This happens because the generated <altmember/> is bad. ↩