Drop php 7.3 support

The rest of the eco system is moving forward, so we can drop php 7.3 now.
The number of installations is really low on 7.3. For the 7.3 people we can still
have v1.x

Author: jaapio

composer.json

@@ -10,7 +10,7 @@
         }
     ],
     "require": {
-        "php": "^7.3 || ^8.0",
+        "php": "^7.4 || ^8.0",
         "phpdocumentor/reflection-common": "^2.0",
         "phpstan/phpdoc-parser": "^2.0",
         "doctrine/deprecations": "^1.0"