Fix switching bold option on and off alters text thickness

Currently, unselecting the bold option resets the thickness to the
standard size instead of reverting to the original thickness.
To address this, the original thickness should be preserved so it
can be restored when bold is turned off.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/18975

common/eda_text.cpp

@@ -249,9 +249,24 @@ void EDA_TEXT::SetBold( bool aBold )
             const int size = std::min( m_attributes.m_Size.x, m_attributes.m_Size.y );
 
             if( aBold )
+            {
+                m_attributes.m_StoredStrokeWidth = m_attributes.m_StrokeWidth;
                 m_attributes.m_StrokeWidth = GetPenSizeForBold( size );
+            }
             else
-                m_attributes.m_StrokeWidth = GetPenSizeForNormal( size );
+            {
+                // Restore the original stroke width from `m_StoredStrokeWidth` if it was previously stored,
+                // resetting the width after unbolding.
+                if( m_attributes.m_StoredStrokeWidth )
+                    m_attributes.m_StrokeWidth = m_attributes.m_StoredStrokeWidth;
+                else
+                {
+                    m_attributes.m_StrokeWidth = GetPenSizeForNormal( size );
+                    // Sets `m_StrokeWidth` to the normal pen size and stores it in `m_StoredStrokeWidth`
+                    // as the default, but only if the bold option was applied before this feature was implemented.
+                    m_attributes.m_StoredStrokeWidth = m_attributes.m_StrokeWidth;
+                }
+            }
         }
         else
         {

common/font/text_attributes.cpp

@@ -35,7 +35,8 @@ TEXT_ATTRIBUTES::TEXT_ATTRIBUTES( KIFONT::FONT* aFont ) :
     m_Visible( true ),
     m_Mirrored( false ),
     m_Multiline( true ),
-    m_KeepUpright( false )
+    m_KeepUpright( false ),
+    m_StoredStrokeWidth( 0 )
 {
 }
 

include/font/text_attributes.h

@@ -145,6 +145,7 @@ public:
 
     // If true, keep rotation angle between -90...90 degrees for readability
     bool              m_KeepUpright;
+    int               m_StoredStrokeWidth;
 };