[9.x] Adds isEqual to compare file hashes in filesystem

[DarkGhostHunter]

What?

Allows to compare two files if these exists and their hashes are the same.

use Illuminate\Support\Facades\File;

if (File::isEqual('foo.txt', 'bar.txt')) {
   return 'Both files are equal.'
}

It will always return false if one of the compared files doesn't exist.

Why?

Useful to check if a file copied was later edited without using exists() and hash() damn every time.

BC?

Is not expected the developer to have a macro of the same name for different functionality.

[vlakoff]

Notes:

• The method has been named hasSameHash(), instead of the initially proposed isEqual().
• It has been followed up by [10.x] Switch to hash_equals in File::hasSameHash() #49721.

[vlakoff]

Now that we can replace MD5 with xxh128, I have submitted PR #54690.