[GTK4] Implement Combo.paste

[akurtakov]

It shouldn't call GTK 3 function (causes a crash right now) and same approach as cut/copy is used.

[github-actions]

Test Results

   408 files   -   137     408 suites   - 137   20m 47s ⏱️ - 13m 42s
 4 343 tests  -    37   4 327 ✅  -    35   16 💤  -  2  0 ❌ ±0 
12 542 runs   - 4 108  12 428 ✅  - 4 081  114 💤  - 27  0 ❌ ±0 

Results for commit f09d0ca. ± Comparison against base commit a13a22d.

This pull request removes 37 tests.

AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicASCII_dollarSign
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicASCII_emptyString
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicASCII_letterA
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicASCII_letters
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16LE_null
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16_AsciiLetters
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16_Asciiletter
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16_LotsOfLetters
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16_letter
AllGTKTests org.eclipse.swt.tests.gtk.Test_GtkConverter ‑ test_HeuristicUTF16_letters
…

♻️ This comment has been updated with latest results.

[akurtakov]

Fixes #1837 linkage error . It doesn't function proper although similar C snippet works just fine:

#include <gtk/gtk.h>

GtkWidget *window;
GtkWidget *combo;
GtkWidget *combo2;
GtkWidget *cut;
GtkWidget *box;

static void
cutpaste (GtkWidget *widget,
             gpointer   data)
{
	GtkWidget *entry;
	GtkWidget *entry2;
	entry = gtk_combo_box_get_child(GTK_COMBO_BOX(combo));
	gtk_widget_activate_action(gtk_widget_get_first_child(GTK_WIDGET(entry)), "clipboard.cut", NULL);
	entry2 = gtk_combo_box_get_child(GTK_COMBO_BOX(combo2));
	gtk_widget_activate_action(gtk_widget_get_first_child(GTK_WIDGET(entry2)), "clipboard.paste", NULL);
}

static void activate(GtkApplication *app, gpointer user_data) {

	window = gtk_application_window_new(app);
	gtk_window_set_title(GTK_WINDOW(window), "Hello");
	gtk_window_set_default_size(GTK_WINDOW(window), 200, 200);

	combo = gtk_combo_box_text_new_with_entry();
	combo2 = gtk_combo_box_text_new_with_entry();
	gtk_combo_box_text_insert(GTK_COMBO_BOX_TEXT(combo), 0, "test", "proba");
	gtk_combo_box_set_active(GTK_COMBO_BOX(combo), 0);

//  gtk_widget_activate_action(GTK_WIDGET(button), "clipboard.paste", NULL);
	cut = gtk_button_new_with_label("cut");
	g_signal_connect(cut, "clicked", G_CALLBACK (cutpaste), NULL);
	box = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 1);
	gtk_box_append(GTK_BOX(box), combo);
	gtk_box_append(GTK_BOX(box), cut);
	gtk_box_append(GTK_BOX(box), combo2);
	gtk_window_set_child(GTK_WINDOW(window), box);

	gtk_window_present(GTK_WINDOW(window));
}

int main(int argc, char **argv) {
	GtkApplication *app;
	int status;

	app = gtk_application_new("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
	g_signal_connect(app, "activate", G_CALLBACK (activate), NULL);
	status = g_application_run(G_APPLICATION(app), argc, argv);
	g_object_unref(app);

	return status;
}

Merging as non functional paste is still better than hard crash.