launcher: wire cancel->reject in C++; document glslang for Windows (#663)

uic from Qt 6.12.0 crashes (0xC0000005) on any non-empty <connections>
block in .ui files. Move the cancel_button -> reject connection from
configuration_edit_dialog.ui into configurationEditDialog.cpp, matching
how the other buttons are already connected there.

Also document the glslang (glslangValidator) requirement for Windows
builds; CMake requires it via find_program(... REQUIRED).

src/launcher/forms/configuration_edit_dialog.ui

@@ -329,12 +329,4 @@
   </customwidget>
  </customwidgets>
  <resources/>
- <connections>
-  <connection>
-   <sender>cancel_button</sender>
-   <signal>clicked()</signal>
-   <receiver>ConfigurationEditDialog</receiver>
-   <slot>reject()</slot>
-  </connection>
- </connections>
 </ui>

src/launcher/src/configurationEditDialog.cpp

@@ -108,6 +108,7 @@ ConfigurationEditDialog::ConfigurationEditDialog(Configuration& info, QWidget* p
 	InitGameDirectories();
 
 	connect(m_ui->ok_button, &QPushButton::clicked, this, &ConfigurationEditDialog::save);
+	connect(m_ui->cancel_button, &QPushButton::clicked, this, &QDialog::reject);
 	connect(m_ui->clear_button, &QPushButton::clicked, this, &ConfigurationEditDialog::clear);
 	connect(m_ui->comboBox_shader_log_direction, &QComboBox::currentTextChanged, this,
 	        [this](const QString& text) {