Define sampleCount as a class, not a type alias...

... Define lots of operators for disambiguation, but they will go away after
all conversions from sampleCount to built-in numerical types are forced
to be explicit.

src/Dependencies.cpp

@@ -143,7 +143,7 @@ void FindDependencies(AudacityProject *project,
             outAliasedFiles.back() =
                AliasedFile {
                   wxFileNameWrapper { fileName },
-                  blockBytes, fileName.FileExists()
+                  wxLongLong(blockBytes), fileName.FileExists()
                };
             aliasedFileHash[fileNameStr] = &outAliasedFiles.back();
          }