Fix hardcoded fonts scaling issues (#7493)

* changed font sizes to better values

* rename gui_templates.h to FontHelper.h

* replace hardcoded values with constants

* make knob labels use small font

* code review from michael

* more consolidation

* Fix text problem in Vectorscope

Fix a problem with cutoff text in Vectorscope. During the constructor
call of `LedCheckBox` the method `LedCheckBox::onTextUpdated` is
triggered which sets a fixed size that fits the pixmap and the text.
After instantiating the two instances in `VecControlsDialog` the
constructor then set a minimum size which overrode the fixed size that
was previously set. This then led to text that was cutoff.

---------

Co-authored-by: Michael Gregorius <michael.gregorius.git@arcor.de>

include/FontHelper.h

@@ -1,5 +1,5 @@
 /*
- * gui_templates.h - GUI-specific templates
+ * FontHelper.h - Header function to help with fonts
  *
  * Copyright (c) 2005-2008 Tobias Doerffel <tobydox/at/users.sourceforge.net>
  *
@@ -22,12 +22,16 @@
  *
  */
 
-#ifndef LMMS_GUI_TEMPLATES_H
-#define LMMS_GUI_TEMPLATES_H
+#ifndef LMMS_FONT_HELPER_H
+#define LMMS_FONT_HELPER_H
 
 #include <QApplication>
 #include <QFont>
 
+constexpr int DEFAULT_FONT_SIZE = 12;
+constexpr int SMALL_FONT_SIZE = 10;
+constexpr int LARGE_FONT_SIZE = 14;
+
 namespace lmms::gui
 {
 
@@ -40,4 +44,4 @@ inline QFont adjustedToPixelSize(QFont font, int size)
 
 } // namespace lmms::gui
 
-#endif // LMMS_GUI_TEMPLATES_H
+#endif // LMMS_FONT_HELPER_H