vala 0.44.1 release.

Various improvements and bug fixes:

• ccodegen:
  • Use unsigned default value for flags-enum
  • Use guint to represent flags-enum in custom GMarshalFunc
• Move disconnect error from signal-module to semantic-analyzer pass
• Mark defined constructors of abstract classes as protected
• parser: Implicit creation method of abstract classes must be protected
• vala: Allow assignment of 0U to enum types
• libvaladoc: Don't try to create a Content.ListItem when there is none

Bindings:

• gio-2.0: SocketAddress.from_native() is a factory method not a constructor
• glib-2.0: Add string.validate_len() since 2.60
• gstreamer: Update from 1.15.2+ git master
• gtk4: Update to 3.94.0+f14d998c
• libgvc: Some additions and ownership/return-type fixes
• vte-2.90: Mark as deprecated, it was replaced by vte-2.91
• vapi: Update GIR-based bindings