Fix badly formed deprecation xml comments

[JanKrivanek]

Fixes https://github.com/orgs/dotnet/projects/117/views/21?pane=issue&itemId=67244195

Context

The deprecation messages have <xref> tag within <summary> tag - this is invalid. A CDATA or <see> tag should have been used instead

Changes Made

Bulk replaced the invalid xmls in <summary> sections:

    /// <xref:Microsoft.Build.Construction>
    /// <xref:Microsoft.Build.Evaluation>
    /// <xref:Microsoft.Build.Execution>

with

 <see href="/dotnet/api/microsoft.build.construction">Microsoft.Build.Construction</see>
  ...