Escape all identifier interpolations in the legacy SQLite translator

Apply quote_identifier() (backtick quoting with internal escaping) to
all table names, column names, index names, and trigger names that are
interpolated into SQL queries, token values, or DDL reconstruction
output. Use PDO::quote() for string arguments to pragma functions.

Fix two downstream issues caused by the quoting style change:
- get_autoincrement_column() regex now accepts both backtick and
  double-quote delimiters in stored schemas.
- CHANGE COLUMN schema parsing now matches both TYPE_SYMBOL (backtick)
  and TYPE_STRING (double-quote) tokens.

Author: JanJakes

tests/WP_SQLite_Translator_Tests.php

@@ -1170,14 +1170,14 @@ public function testColumnWithOnUpdate() {
 					'name'     => '___tmp_table_created_at_on_update__',
 					'tbl_name' => '_tmp_table',
 					'rootpage' => '0',
-					'sql'      => "CREATE TRIGGER \"___tmp_table_created_at_on_update__\"\n\t\t\tAFTER UPDATE ON \"_tmp_table\"\n\t\t\tFOR EACH ROW\n\t\t\tBEGIN\n\t\t\t  UPDATE \"_tmp_table\" SET \"created_at\" = CURRENT_TIMESTAMP WHERE rowid = NEW.rowid;\n\t\t\tEND",
+					'sql'      => "CREATE TRIGGER `___tmp_table_created_at_on_update__`\n\t\t\tAFTER UPDATE ON `_tmp_table`\n\t\t\tFOR EACH ROW\n\t\t\tBEGIN\n\t\t\t  UPDATE `_tmp_table` SET `created_at` = CURRENT_TIMESTAMP WHERE rowid = NEW.rowid;\n\t\t\tEND",
 				),
 				(object) array(
 					'type'     => 'trigger',
 					'name'     => '___tmp_table_updated_at_on_update__',
 					'tbl_name' => '_tmp_table',
 					'rootpage' => '0',
-					'sql'      => "CREATE TRIGGER \"___tmp_table_updated_at_on_update__\"\n\t\t\tAFTER UPDATE ON \"_tmp_table\"\n\t\t\tFOR EACH ROW\n\t\t\tBEGIN\n\t\t\t  UPDATE \"_tmp_table\" SET \"updated_at\" = CURRENT_TIMESTAMP WHERE rowid = NEW.rowid;\n\t\t\tEND",
+					'sql'      => "CREATE TRIGGER `___tmp_table_updated_at_on_update__`\n\t\t\tAFTER UPDATE ON `_tmp_table`\n\t\t\tFOR EACH ROW\n\t\t\tBEGIN\n\t\t\t  UPDATE `_tmp_table` SET `updated_at` = CURRENT_TIMESTAMP WHERE rowid = NEW.rowid;\n\t\t\tEND",
 				),
 			),
 			$results