[mssql] Support delimited identifiers in [square brackets]

T-SQL supports non-standard `[...]` quoting in addition to the widely
supported and standard `"..."`:

https://docs.microsoft.com/en-us/sql/relational-databases/databases/database-identifiers?view=sql-server-2017

src/dialect/mssql.rs

@@ -4,6 +4,10 @@ use crate::dialect::Dialect;
 pub struct MsSqlDialect {}
 
 impl Dialect for MsSqlDialect {
+    fn is_delimited_identifier_start(&self, ch: char) -> bool {
+        ch == '"' || ch == '['
+    }
+
     fn is_identifier_start(&self, ch: char) -> bool {
         // See https://docs.microsoft.com/en-us/sql/relational-databases/databases/database-identifiers?view=sql-server-2017#rules-for-regular-identifiers
         // We don't support non-latin "letters" currently.

tests/sqlparser_mssql.rs

@@ -27,7 +27,14 @@ fn parse_mssql_identifiers() {
     };
 }
 
-#[allow(dead_code)]
+#[test]
+fn parse_mssql_delimited_identifiers() {
+    let _ = ms().one_statement_parses_to(
+        "SELECT [a.b!] [FROM] FROM foo [WHERE]",
+        "SELECT [a.b!] AS [FROM] FROM foo AS [WHERE]",
+    );
+}
+
 fn ms() -> TestedDialects {
     TestedDialects {
         dialects: vec![Box::new(MsSqlDialect {})],