Improve wxRadioBox width on wxMSW

Do not use 'RADIO_SIZE 20' as the fixed width of the radio button, but use the actual width as returned by wxRendererNative.
wxRendererNative has no GetRadioButtonSize, so for now use GetCheckBoxSize. It returns the same sizes.
Also add a half character width to account for the space between the button and the label.
There is no need to add extra width to the label of the static box.

Closes #18010.

include/wx/msw/private.h

@@ -100,7 +100,6 @@ WXDLLIMPEXP_BASE void wxSetInstance(HINSTANCE hInst);
 #define CHECK_IS_FAFA    FALSE
 #define RADIO_CLASS      wxT("BUTTON")
 #define RADIO_FLAGS      (BS_AUTORADIOBUTTON|WS_CHILD|WS_VISIBLE)
-#define RADIO_SIZE       20
 #define RADIO_IS_FAFA    FALSE
 #define PURE_WINDOWS
 #define GROUP_CLASS      wxT("BUTTON")

src/msw/radiobox.cpp

@@ -36,6 +36,7 @@
 #endif
 
 #include "wx/msw/subwin.h"
+#include "wx/renderer.h"
 
 #if wxUSE_TOOLTIPS
     #include "wx/tooltip.h"
@@ -549,6 +550,15 @@ WX_FORWARD_STD_METHODS_TO_SUBWINDOWS(wxRadioBox, wxStaticBox, m_radioButtons)
 
 wxSize wxRadioBox::GetMaxButtonSize() const
 {
+    // We use GetCheckBox() because there is no dedicated GetRadioBox() method
+    // in wxRendererNative, but check and radio boxes are usually of the same
+    // size anyhow. We also add half a character of width to account for the
+    // extra space after the radio box itself.
+    const int radioWidth =
+        wxRendererNative::Get().GetCheckBoxSize(
+            reinterpret_cast<wxWindow*>(const_cast<wxRadioBox*>(this))).x
+        + GetCharWidth() / 2;
+
     // calculate the max button size
     int widthMax = 0,
         heightMax = 0;
@@ -561,8 +571,7 @@ wxSize wxRadioBox::GetMaxButtonSize() const
             GetTextExtent(wxGetWindowText((*m_radioButtons)[i]), &width, &height);
 
             // adjust the size to take into account the radio box itself
-            // FIXME this is totally bogus!
-            width += RADIO_SIZE;
+            width += radioWidth;
             height *= 3;
             height /= 2;
         }
@@ -599,7 +608,6 @@ wxSize wxRadioBox::GetTotalButtonSize(const wxSize& sizeBtn) const
     // and also wide enough for its label
     int widthLabel;
     GetTextExtent(GetLabelText(), &widthLabel, NULL);
-    widthLabel += RADIO_SIZE; // FIXME this is bogus too
     if ( widthLabel > width )
         width = widthLabel;