[CodeComplete] Format SemaCodeComplete.cpp and improve code consistency

There are some mis-indented places and missing spaces here and there. Just format the whole file.

Also, newer code (from 2014 onwards) in this file prefers const auto *X = dyn_cast to not repeat the Decl type name. Make other occurrences consistent.
Remove two anonymous namespaces that are not very necessary: 1) a typedef 2) a local function (should use static)

llvm-svn: 347507