Unify column name representation in stored schema, support all representations when parsing

At the moment, CREATE TABLE statements normalize column names to use double quotes
and they are stored as such in sqlite_master and returned by get_sqlite_create_table().

However, the else branch of CHANGE COLUMN statements was using backticks instead,
which caused incorrect parsing for the next ALTER COLUMN statements now, when some
CHANGE statements without column definition are supported (SET/DROP DEFAULT).

This commit fixes both — 1) the name representation to use double quotes instead of backticks,
and 2) the parsing to support all column name representation (double quotes, backticks, nothing).

Author: JanJakes

wp-includes/sqlite/class-wp-sqlite-translator.php

@@ -3040,8 +3040,21 @@ private function execute_alter() {
 					if ( ! $token ) {
 						break;
 					}
-					if ( WP_SQLite_Token::TYPE_STRING !== $token->type
-						|| $from_name !== $this->normalize_column_name( $token->value ) ) {
+
+					// Column name can be represented as:
+					//   1. "column_name" (string)
+					//   2. `column_name` (symbol)
+					//   3. column_name   (keyword — not a reserved one)
+					// While CREATE TABLE normalizes column names to strings, it's better to handle all
+					// variants to handle table definitions with names stored in any valid form.
+					$is_column_name = WP_SQLite_Token::TYPE_STRING === $token->type
+						|| WP_SQLite_Token::TYPE_SYMBOL === $token->type
+						|| (
+							WP_SQLite_Token::TYPE_KEYWORD === $token->type
+							&& ! ( WP_SQLite_Token::FLAG_KEYWORD_RESERVED & $token->flags )
+						);
+
+					if ( ! $is_column_name || $from_name !== $this->normalize_column_name( $token->value ) ) {
 						continue;
 					}
 
@@ -3076,7 +3089,7 @@ private function execute_alter() {
 						// Otherwise, just add the new name in place of the old name we dropped.
 						$create_table->add(
 							new WP_SQLite_Token(
-								'`' . ( $new_field ? $new_field->name : $from_name ) . '`',
+								'"' . ( $new_field ? $new_field->name : $from_name ) . '"',
 								WP_SQLite_Token::TYPE_KEYWORD
 							)
 						);