Changed all of our synthesized "___clang" functions, types and variables
that get used in expressions over to have a prefix of "$_lldb". Now when we
do name lookups we can easily switch off of the first '$' character to know
if we should look through only our internal (when first char is '$') stuff,
or when we should look through program variables, functions and types.

Converted all of the clang expression code over to using "const ConstString&" 
values for names instead of "const char *" since there were many places that
were converting the "const char *" names into ConstString names and them
throwing them away. We now avoid making a lot of ConstString conversions and
benefit from the quick comparisons in a few extra spots.

Converted a lot of code from LLVM coding conventions into LLDB coding 
conventions.

llvm-svn: 116634