GATE v1.1.0 - Types first, and the editor no longer lies

The first feature release. Most of it is types: unions, tuples, typed callables, aliases
and typed scenes, plus flow typing that makes is narrow and as honest. The rest is the
editor finally treating .gate as a language rather than an unknown file.

Valid GDScript is still valid GATE. Rename a .gd to .gate and it compiles with no
errors, loads, and behaves identically.

New types

• Unions <int | str> and tuples <int, str>, checked at compile time, emitted as
  a plain Variant and Array
• Typed callables func(int) -> bool, checked on assignment and on .call()
• Type aliases type Hp = int, pure substitution with nothing emitted
• Typed scenes PackedScene<Enemy>, so instantiate() has a type
• match type patterns, Circle c: and Rect r when r.w == r.h:
• is narrows, and as is no longer trusted inside GATE's own declarations

In the editor

• .gate files appear in the FileSystem dock with their own icon, open in the real script
  editor with GATE's colours, and can be created from the UI
• Autocompletion, Ctrl-click and F1, and breakpoints that stop the running game and show
  the stop in the .gate rather than the generated .gd
• Godot's own warnings, unused variable, unused parameter, shadowed name and the rest,
  reported against the .gate in Godot's own words, honouring your warning settings
• Generated output is indented the way your project is

Also

• Swizzling, object initialisers, @required, @export_if, and signal emit and connect
  checks
• Struct value semantics fixed throughout: copies where they are received, defaults that
  run once, field-wise ==
• A build now does only what your edit changed, and an unchanged project builds nothing
• Eighteen superset violations fixed, one of them a wrong value in 1.0.x

Requires Godot 4.7. Full detail in CHANGELOG.md, and what comes next is in
ROADMAP.md.