Add new SQL parser to support S3 Select syntax (#7102)

- New parser written from scratch, allows easier and complete parsing
  of the full S3 Select SQL syntax. Parser definition is directly
  provided by the AST defined for the SQL grammar.

- Bring support to parse and interpret SQL involving JSON path
  expressions; evaluation of JSON path expressions will be
  subsequently added.

- Bring automatic type inference and conversion for untyped
  values (e.g. CSV data).

vendor/github.com/alecthomas/participle/lexer/doc.go

@@ -0,0 +1,19 @@
+// Package lexer defines interfaces and implementations used by Participle to perform lexing.
+//
+// The primary interfaces are Definition and Lexer. There are three implementations of these
+// interfaces:
+//
+// TextScannerLexer is based on text/scanner. This is the fastest, but least flexible, in that
+// tokens are restricted to those supported by that package. It can scan about 5M tokens/second on a
+// late 2013 15" MacBook Pro.
+//
+// The second lexer is constructed via the Regexp() function, mapping regexp capture groups
+// to tokens. The complete input source is read into memory, so it is unsuitable for large inputs.
+//
+// The final lexer provided accepts a lexical grammar in EBNF. Each capitalised production is a
+// lexical token supported by the resulting Lexer. This is very flexible, but a bit slower, scanning
+// around 730K tokens/second on the same machine, though it is currently completely unoptimised.
+// This could/should be converted to a table-based lexer.
+//
+// Lexer implementations must use Panic/Panicf to report errors.
+package lexer