Fix LoginStatementTests - handle national strings and IsIfExists

- Add IsIfExists field to DropLoginStatement
- Fix national string handling: strip N prefix and quotes from value
- Enable LoginStatementTests and Baselines90_LoginStatementTests

Author: claude

ast/create_simple_statements.go

@@ -54,7 +54,8 @@ func (s *AlterLoginOptionsStatement) statement() {}
 
 // DropLoginStatement represents DROP LOGIN name
 type DropLoginStatement struct {
-	Name *Identifier `json:"Name,omitempty"`
+	Name       *Identifier `json:"Name,omitempty"`
+	IsIfExists bool        `json:"IsIfExists"`
 }
 
 func (s *DropLoginStatement) node()      {}

parser/marshal.go

@@ -15698,7 +15698,8 @@ func alterLoginOptionsStatementToJSON(s *ast.AlterLoginOptionsStatement) jsonNod
 
 func dropLoginStatementToJSON(s *ast.DropLoginStatement) jsonNode {
 	node := jsonNode{
-		"$type": "DropLoginStatement",
+		"$type":      "DropLoginStatement",
+		"IsIfExists": s.IsIfExists,
 	}
 	if s.Name != nil {
 		node["Name"] = identifierToJSON(s.Name)

parser/parse_ddl.go

@@ -6005,13 +6005,19 @@ func (p *Parser) parseAlterLoginOptions(name *ast.Identifier) (*ast.AlterLoginOp
 			// Parse password value
 			if p.curTok.Type == TokenString || p.curTok.Type == TokenNationalString {
 				val := p.curTok.Literal
+				isNational := p.curTok.Type == TokenNationalString
+				// Strip N prefix for national strings
+				if isNational && len(val) > 0 && (val[0] == 'N' || val[0] == 'n') {
+					val = val[1:]
+				}
+				// Strip surrounding quotes
 				if len(val) >= 2 && val[0] == '\'' && val[len(val)-1] == '\'' {
 					val = val[1 : len(val)-1]
 				}
 				opt.Password = &ast.StringLiteral{
 					LiteralType:   "String",
 					Value:         val,
-					IsNational:    p.curTok.Type == TokenNationalString,
+					IsNational:    isNational,
 					IsLargeObject: false,
 				}
 				p.nextToken()

parser/testdata/Baselines90_LoginStatementTests/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/LoginStatementTests/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}