Lexer improvements:

- Convert unquoted idents to lowercase.
- Recognize quoted idents.
- Allow all unicode whitespace characters
- Added UnexpectedSymbol token for unexpected input (otherwise it is just ignored)
- Handle mixed case keywords in the lexer file instead of filtering the stream

pglablib/sqlparser/Parser.cpp

@@ -8,8 +8,7 @@ Parser::Parser(const std::string &input_string)
 
 Parser::Parser(std::unique_ptr<antlr4::CharStream> stream)
     : InputStream(std::move(stream))
-    , CaseFilter(InputStream.get(), true)
-    , Lexer(&CaseFilter)
+    , Lexer(InputStream.get())
     , TokenStream(&Lexer)
     , AParser(&TokenStream)
 {