Create an interactive porting tool

`blueprint-compiler port` interactively ports a project to blueprint.
It will create the subproject wrap file, add it to .gitignore, decompile
your GtkBuilder XML files, emit code to copy and paste into your
meson.build file, and update POTFILES.in.

It can't quite handle all of the features the forward compiler can, so
it will skip those files.

tests/samples/accessibility_dec.blp

@@ -0,0 +1,12 @@
+using Gtk 4.0;
+
+Widget {
+  accessibility {
+    label: _("Hello, world!");
+    labelled_by: my_label;
+    checked: true;
+  }
+}
+
+Label my_label {
+}

tests/samples/id_prop.blp

@@ -4,4 +4,5 @@ Scale {
   adjustment: adj;
 }
 
-Adjustment adj {}
+Adjustment adj {
+}

tests/samples/layout_dec.blp

@@ -0,0 +1,10 @@
+using Gtk 4.0;
+
+Grid {
+  Label {
+    layout {
+      column: "0";
+      row: "1";
+    }
+  }
+}

tests/samples/menu.ui

@@ -25,4 +25,4 @@
       </item>
     </submenu>
   </menu>
-</interface>
+</interface>

tests/samples/menu_dec.blp

@@ -0,0 +1,31 @@
+using Gtk 4.0;
+
+menu {
+  label: _("menu label");
+  test-custom-attribute: "3.1415";
+
+  submenu {
+    section {
+      label: "test section";
+    }
+
+    item {
+      label: "test item";
+    }
+
+    item {
+      label: "test item shorthand 1";
+    }
+
+    item {
+      label: "test item shorthand 2";
+      action: "app.test-action";
+    }
+
+    item {
+      label: "test item shorthand 3";
+      action: "app.test-action";
+      icon: "test-symbolic";
+    }
+  }
+}

tests/samples/style_dec.blp

@@ -0,0 +1,8 @@
+using Gtk 4.0;
+
+Label {
+  styles [
+    "class-1",
+    "class-2",
+  ]
+}

tests/samples/translated.blp

@@ -3,6 +3,7 @@ using Gtk 4.0;
 Label {
   label: _("Hello, world!");
 }
+
 Label {
   label: C_("translation context", "Hello");
 }

tests/samples/using.blp

@@ -1,4 +1,5 @@
 using Gtk 4.0;
 using GObject 2.0;
 
-GObject.Object {}
+GObject.Object {
+}