pw-dump does not escape backslashes

If you are filing this issue with a regular release please try master as it might already be fixed.

Version: 0.3.26
Distribution: Arch Linux
Desktop Environment: sway

Description of Problem: pw-dump does not escape backslash "\", resulting in unwanted characters or invalid escape in the JSON

How Reproducible: always

Steps to Reproduce:

1. Play an mp3 with a backslash in its metadata title
2. pw-dump -N | grep media.title

Actual Results: "media.title": "text\more_text",

Expected Results: "media.title": "text\\more_text",

Additional Info Eg. pw-dump -N > file (As Attachment Please):

pw-dump.json