Follow-up from #11259

This PR reworks the FileSystem::OpenFile call to take a single FileOpenFlags object, instead of the previous three parameters (uint8_t flags, FileLockType lock, FileCompressionType compression). The FileOpenFlags holds all this information and is more future-proof.

unique_ptr<FileHandle> OpenFile(const string &path, FileOpenFlags flags, optional_ptr<FileOpener> opener);

The FileOpenFlags can be bitwise or-d together similar to the previous flags, and it can also be bitwise or-ed with the FileLockType and FileCompressionType, i.e. this now works:

file = fs.OpenFile(file_name, FileFlags::FILE_FLAGS_READ | FileLockType::READ_LOCK | FileCompressionType::AUTO_DETECT);

Instead of doing bitwise operations, there are now methods that can be used to access various properties, e.g. flags.OpenForWriting() instead of flags & FileFlags::FILE_FLAGS_WRITE.

FILE_FLAGS_NULL_IF_NOT_EXISTS

This PR adds a new flag to OpenFile - FILE_FLAGS_NULL_IF_NOT_EXISTS. When this is passed into OpenFile, a nullptr is returned when the file cannot be opened because it does not exist, instead of throwing an exception. This allows for this pattern:

if (fs.FileExists(file_name)) {
	auto handle = fs.OpenFile(file_name, ...);
	...
}

To be replaced with this pattern:

auto handle = fs.OpenFile(file_name, FileFlags::FILE_FLAGS_NULL_IF_NOT_EXISTS | ...)
if (handle) {
	...
}

This has the following benefits:

• It prevents an OS-level race-condition (FileExists -> OpenFile has an obvious race where the file can be removed in between calls)
• It is more performant (we do a single OS call instead of two). This is not very relevant for local file systems, but is actually very relevant for remote file systems, as FileExists is very expensive for HTTPFS/S3FS/etc.

Using this new pattern for the write-ahead log fixes #9342, which was caused by precisely such a race (where FileExists would return true, followed by OpenFile failing because the file did not exist).