852cc9200f
`FindNamespace` was not implemented for `SymbolFileNativePDB`. Without it, it wasn't possible to lookup items through namespaces when evaluating expressions. This is mostly the same as in [SymbolFilePDB](f1eb869bae/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp (L1664-L1696)) as well as [PDBAstParser](f1eb869bae/lldb/source/Plugins/SymbolFile/PDB/PDBASTParser.cpp (L1126-L1150)): The AST parser/builder saves the created namespaces in a map to lookup when a namespace is requested. This is working towards making [Shell/SymbolFile/PDB/expressions.test](f1eb869bae/lldb/test/Shell/SymbolFile/PDB/expressions.test) pass with the native PDB plugin.