Remove shadow tables from database dump

[groue]

This pull request fixes #1464 by not recording shadow tables from dumpContent(format:to:).

Shadow tables are implementation details of virtual tables (FTS4, FTS5, ...) that do not provide useful information in database dumps.

---

Caveat: detection of shadow tables uses PRAGMA table_list and requires SQLite 3.37+ (iOS 15.4, macOS 12.4, tvOS 15.4, watchOS 8.5). When run with older SQLite versions, shadow tables are still recorded.

This might bother applications that use the GRDBSnapshotTesting companion library, because the test results change, depending on the SQLite version 😬

A possible solution is to skip those tests until SQLite 3.37+, as in the sample code below:

import GRDB
import GRDBSnapshotTesting
import InlineSnapshotTesting
import XCTest

class MyDatabaseTests: XCTestCase {
    func test_full_database_content() throws {
        // Database snapshot contains undesired shadow tables
        // unless we run SQLite 3.37+.
        guard sqlite3_libversion_number() >= 3037000 else {
            throw XCTSkip("Can't snapshot database before SQLite 3.37")
        }
        
        let dbQueue = try makeMyDatabase()
        assertInlineSnapshot(of: dbQueue, as: .dumpContent()) {
            ...
        }
    }
}