Allow keywords as WITH clause aliases

In scalar WITH clauses like `WITH expr AS name`, the alias can now be
a keyword (e.g., `key`, `values`) in addition to regular identifiers.
This matches ClickHouse's behavior.

This fixes 20+ statements across multiple tests including:
- 02124_encrypt_decrypt_nullable
- 03254_timeseries_to_grid_aggregate_function (various)
- 03205_overlay
- 01930_optimize_skip_unused_shards_rewrite_in

Author: claude

parser/parser.go

@@ -1057,7 +1057,8 @@ func (p *Parser) parseWithClause() []ast.Expression {
 			// AS name is optional
 			if p.currentIs(token.AS) {
 				p.nextToken()
-				if p.currentIs(token.IDENT) {
+				// Alias can be IDENT or certain keywords (KEY, VALUES, etc.)
+				if p.currentIs(token.IDENT) || p.current.Token.IsKeyword() {
 					elem.Name = p.current.Value
 					p.nextToken()
 				}

parser/testdata/01214_point_in_Mecca/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt67": true
-  }
-}
+{}

parser/testdata/01318_decrypt/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt47": true
-  }
-}
+{}

parser/testdata/01318_encrypt/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt46": true
-  }
-}
+{}

parser/testdata/01930_optimize_skip_unused_shards_rewrite_in/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt3": true
-  }
-}
+{}

parser/testdata/02124_encrypt_decrypt_nullable/metadata.json

@@ -1,14 +1 @@
-{
-  "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt13": true,
-    "stmt14": true,
-    "stmt15": true,
-    "stmt16": true,
-    "stmt3": true,
-    "stmt6": true,
-    "stmt8": true,
-    "stmt9": true
-  }
-}
+{}

parser/testdata/03205_overlay/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt35": true
-  }
-}
+{}

parser/testdata/03254_timeseries_functions/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt5": true,
-    "stmt6": true,
-    "stmt7": true
-  }
-}
+{}

parser/testdata/03254_timeseries_to_grid_aggregate_function/metadata.json

@@ -1,11 +1,6 @@
 {
   "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt12": true,
     "stmt2": true,
-    "stmt3": true,
-    "stmt8": true,
-    "stmt9": true
+    "stmt3": true
   }
 }

parser/testdata/03254_timeseries_to_grid_aggregate_function_sparse/metadata.json

@@ -1,12 +1,6 @@
 {
   "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt12": true,
-    "stmt13": true,
     "stmt2": true,
-    "stmt3": true,
-    "stmt8": true,
-    "stmt9": true
+    "stmt3": true
   }
 }