First stage of cleaning up the export handling of the slint root component (#2095)

We implicitly export the last component of a .slint file to the generator.
Issue a warning when that happens and suggest to export it explicitly.

internal/compiler/tests/syntax/analysis/binding_loop1.slint

@@ -14,7 +14,7 @@ WithStates := Rectangle {
     ]
 }
 
-Test := Rectangle {
+export Test := Rectangle {
 
     property <int> a: 45 + root.b;
     //               ^error{The binding for the property 'a' is part of a binding loop}

internal/compiler/tests/syntax/analysis/binding_loop2.slint

@@ -35,7 +35,7 @@ T4 := Rectangle {
     property <length> my_property <=> x;
 }
 
-App := Rectangle {
+export App := Rectangle {
 
 
     VerticalLayout {

internal/compiler/tests/syntax/analysis/binding_loop_function.slint

@@ -18,7 +18,7 @@ Compo1 := Rectangle {
 //  ^error{The binding for the property 'bb' is part of a binding loop}
 }
 
-App := Rectangle {
+export App := Rectangle {
     cc := Compo1 {
         aa() => { return self.a; }
 //      ^error{The binding for the property 'aa' is part of a binding loop}
@@ -29,4 +29,4 @@ App := Rectangle {
 
 
 
-}
+}

internal/compiler/tests/syntax/analysis/binding_loop_issue_772.slint

@@ -6,7 +6,7 @@ Alias := Rectangle {
     property <int> ps_width <=> viewport_width;
 }
 
-Foo := Rectangle {
+export Foo := Rectangle {
     property <int> base-prop: alias.viewport_width;
     //                       ^error{The binding for the property 'base-prop' is part of a binding loop}
 

internal/compiler/tests/syntax/analysis/binding_loop_layout.slint

@@ -19,7 +19,7 @@ TC := Rectangle {
 }
 
 
-Test := Rectangle {
+export Test := Rectangle {
     VerticalLayout {
 //  ^error{The binding for the property 'layoutinfo-h' is part of a binding loop}  // FIXME: That's an internal property, but people might understand
 //  ^^error{The binding for the property 'min-width' is part of a binding loop}

internal/compiler/tests/syntax/analysis/binding_loop_layout2.slint

@@ -26,7 +26,7 @@ Wrap := Rectangle {
     property <bool> test: square.width == square.height;
 }
 
-Test := Rectangle {
+export Test := Rectangle {
     property <image> source;
     GridLayout {
 //  ^error{The binding for the property 'layout-cache-h' is part of a binding loop}

internal/compiler/tests/syntax/analysis/binding_loop_layout3.slint

@@ -22,7 +22,7 @@ Compo := Rectangle {
 
 }
 
-Foo := Rectangle {
+export Foo := Rectangle {
     Compo {
 //  ^error{The binding for the property 'preferred-width' is part of a binding loop}
         the_text: self.preferred-width / 1px;

internal/compiler/tests/syntax/analysis/binding_loop_self.slint

@@ -5,7 +5,7 @@
 
 Key := Rectangle { property <int> pos; property <int> num_elements; }
 
-Test := Rectangle {
+export Test := Rectangle {
     Rectangle {
         property <int> num_elements;
         num-elements: 4;