info: add di_info_get_device_tag()

This is a new iteration of !115 (closed). More things are baked into the string:

• Model and serial codes are always baked in, because some EDIDs have identical strings but different codes (wlroots/wlroots#3913).
• Manufacture year + week, because I found ~410 cases in linuxhw/EDID where this helped.
• Unspecified ASCII string, because I found ~400 cases in linuxhw/EDID where this helped.

Small script to find duplicates in linuxhw/EDID

import os
import subprocess

tags = {}
for root, dirs, files in os.walk('../linuxhw-EDID/Digital'):
    for name in files:
        path = root + '/' + name

        with open(path) as f:
            raw = f.read()

        raw = raw.replace('edid-decode (hex):', '')
        raw = raw.split('---', 2)[0]
        raw = raw.replace(' ', '').replace('\n', '')

        try:
            blob = bytes.fromhex(raw)
        except ValueError:
            print('MALFORMED: ' + path)
            continue

        result = subprocess.run(['build/test/di-edid-print'], input=blob, capture_output=True)

        if result.returncode != 0:
            print('ERROR: ' + path)
            print(result.stderr.decode('utf-8'))
        else:
            tag = None
            for l in result.stdout.decode('utf-8').split('\n'):
                if l.startswith('device tag:'):
                    tag = l.split(':', 2)[1].strip()
            assert(tag != None)

            matches = tags.get(tag, [])
            matches.append(path)
            tags[tag] = matches

ndupes = 0
for tag in tags:
    matches = tags[tag]
    if len(matches) > 1:
        ndupes += 1
        print(tag, matches)

print('Number of duplicates:', ndupes)

cc @pq @Zamundaaa