[Index] Don't replace ' ' or '-' in group names when mapping them to a 'module' name.

The fake module names we create when indexing a Swift module divided into
'groups' (e.g. the stdlib) don't have to be valid Swift module names, but we
were manipulating them to be so. E.g. the stdlib "Lazy Views" group, became
"Lazy_Views". This name is displayed in some editors verbatim, and is also
used as input to some sourcekitd APIs (e.g. editor.open.interface) that only
work if the original group name is passed, rather than the processed one.

This patch stops mapping invalid module name characters like ' ' and '-' to '_'
so the original group name remains.

Resolves rdar://problem/57270811

Author: Nathan Hawes

lib/Index/IndexRecord.cpp

@@ -514,8 +514,6 @@ emitDataForSwiftSerializedModule(ModuleDecl *module,
       for (char ch : groupName) {
         if (ch == '/')
           buf += '.';
-        else if (ch == ' ' || ch == '-')
-          buf += '_';
         else
           buf += ch;
       }