Register default port for common internet schema

[mkykadir]

Separates default port from URL and ties default port to common internet schema. Default behavior of URL.defaultPort is kept (returns 0 for unknown schemas). Built-in schemas are registered at init.

Changes

• StringSet renamed and converted to ushort[string] map
• Built-in schemas are registered as common internet schemas
• New function implemented for getting default port of a registered common internet schema

Decision points before merge

• ✅ registerCommonInternetSchema can throw exception when schema is already registered within built-in schemas (or user schemas, user schemas can be updated silently) -> Schemas will be updated silently
• ✅ getDefaultPortOfCommonInternetSchema can be nothrow (thus @nogc) and return 0 directly