Create basic escaped unicode decoder

[rgmz]

Description:

This creates a decoder to handle basic unicode escaped sequences (\u1234).

TODO:

• [ ] Handle other formats like \u12 or U+1234
• [ ] Restrict which characters get changed (e.g. it's advantageous to handle [[:graph:]] but not emojis)
• [ ] Test "in the field" to see whether this generates false-positives

Checklist:

• [ ] Tests passing (make test-community)?
• [ ] Lint passing (make lint this requires golangci-lint)?