Add wxWindow::WXAdjustFontToOwnPPI()

Avoid calling GeTDPI() in font.WXAdjustToPPI(GetDPI()); invocations in
common code on platforms that don't need any adjustment (i.e. anything
other than MSW).

This fixes wxOSX crashes when GetFont() is called too early during
window creation, but is the right thing to do regardless.

Closes https://github.com/wxWidgets/wxWidgets/pull/2036

Closes #18903.

src/common/wincmn.cpp

@@ -1710,7 +1710,7 @@ wxFont wxWindowBase::GetFont() const
         if ( !font.IsOk() )
             font = GetClassDefaultAttributes().font;
 
-        font.WXAdjustToPPI(GetDPI());
+        WXAdjustFontToOwnPPI(font);
 
         return font;
     }
@@ -1731,7 +1731,7 @@ bool wxWindowBase::SetFont(const wxFont& font)
     m_inheritFont = m_hasFont;
 
     if ( m_hasFont )
-        m_font.WXAdjustToPPI(GetDPI());
+        WXAdjustFontToOwnPPI(m_font);
 
     InvalidateBestSize();
 

src/msw/window.cpp

@@ -4864,6 +4864,11 @@ double wxWindowMSW::GetDPIScaleFactor() const
     return GetDPI().y / (double)wxDisplay::GetStdPPIValue();
 }
 
+void wxWindowMSW::WXAdjustFontToOwnPPI(wxFont& font) const
+{
+    font.WXAdjustToPPI(GetDPI());
+}
+
 void wxWindowMSW::MSWUpdateFontOnDPIChange(const wxSize& newDPI)
 {
     if ( m_font.IsOk() )