Clean and unify pad/fp rotations

IPC2581 classifies pad rotation as clockwise from the top layer looking
down.  Which means that if you have the exact same footprint with
rotated pads on the top layer and bottom layer, then that will need two
different packages because one package will have the pads rotated one
way, the other will have the pads rotated in the opposite direction.
The IPC committee clearly was too smart for its own good here.  So we
hash the footprints based on layer as well and then introduce the
rotation into the pad.  This increases the number of packages but keeps
the code compact

Fixes https://gitlab.com/kicad/code/kicad/-/issues/19703

pcbnew/pcb_io/ipc2581/pcb_io_ipc2581.cpp

@@ -1243,10 +1243,6 @@ wxXmlNode* PCB_IO_IPC2581::generateBOMSection( wxXmlNode* aEcadNode )
         std::unique_ptr<FOOTPRINT> fp( static_cast<FOOTPRINT*>( fp_it->Clone() ) );
         fp->SetParentGroup( nullptr );
         fp->SetPosition( {0, 0} );
-
-        if( fp->GetLayer() != F_Cu )
-            fp->Flip( fp->GetPosition(), FLIP_DIRECTION::TOP_BOTTOM );
-
         fp->SetOrientation( ANGLE_0 );
 
         size_t hash = hash_fp_item( fp.get(), HASH_POS | REL_COORD );
@@ -1800,11 +1796,9 @@ void PCB_IO_IPC2581::addPad( wxXmlNode* aContentNode, const PAD* aPad, PCB_LAYER
     if( aPad->GetOrientation() != ANGLE_0 )
     {
         wxXmlNode* xformNode = appendNode( padNode, "Xform" );
-        xformNode->AddAttribute( "rotation",
-                                 floatVal( aPad->GetOrientation().Normalize().AsDegrees() ) );
+        EDA_ANGLE angle = aPad->GetOrientation().Normalize();
 
-        if( fp && fp->IsFlipped() )
-            addAttribute( xformNode,  "mirror", "true" );
+        xformNode->AddAttribute( "rotation", floatVal( angle.AsDegrees() ) );
     }
 
     addLocationNode( padNode, *aPad, false );
@@ -2133,10 +2127,6 @@ wxXmlNode* PCB_IO_IPC2581::addPackage( wxXmlNode* aContentNode, FOOTPRINT* aFp )
     std::unique_ptr<FOOTPRINT> fp( static_cast<FOOTPRINT*>( aFp->Clone() ) );
     fp->SetParentGroup( nullptr );
     fp->SetPosition( { 0, 0 } );
-
-    if( fp->GetLayer() != F_Cu )
-        fp->Flip( fp->GetPosition(), FLIP_DIRECTION::TOP_BOTTOM );
-
     fp->SetOrientation( ANGLE_0 );
 
     size_t hash = hash_fp_item( fp.get(), HASH_POS | REL_COORD );
@@ -2403,12 +2393,16 @@ wxXmlNode* PCB_IO_IPC2581::addPackage( wxXmlNode* aContentNode, FOOTPRINT* aFp )
         else
             addAttribute( pinNode,  "type", "SURFACE" );
 
-        if( pad->GetFPRelativeOrientation() != ANGLE_0 )
+        if( pad->GetFPRelativeOrientation() != ANGLE_0 )//|| fp->IsFlipped() )
         {
             wxXmlNode* xformNode = appendNode( pinNode, "Xform" );
-            xformNode->AddAttribute(
-                    "rotation",
-                    floatVal( pad->GetFPRelativeOrientation().Normalize().AsDegrees() ) );
+            EDA_ANGLE pad_angle = pad->GetFPRelativeOrientation().Normalize();
+
+            if( fp->IsFlipped() )
+                pad_angle = ( pad_angle.Invert() - ANGLE_180 ).Normalize();
+
+            if( pad_angle != ANGLE_0 )
+                xformNode->AddAttribute( "rotation", floatVal( pad_angle.AsDegrees() ) );
         }
 
         addLocationNode( pinNode, *pad, true );
@@ -2472,19 +2466,19 @@ void PCB_IO_IPC2581::generateComponents( wxXmlNode* aStepNode )
         else
             addAttribute( componentNode,  "mountType", "OTHER" );
 
-        if( fp->GetOrientation() != ANGLE_0 || fp->GetLayer() != F_Cu )
+        if( fp->GetOrientation() != ANGLE_0 || fp->IsFlipped() )
         {
             wxXmlNode* xformNode = appendNode( componentNode, "Xform" );
 
             EDA_ANGLE fp_angle = fp->GetOrientation().Normalize();
 
-            if( fp->GetLayer() == B_Cu )
+            if( fp->IsFlipped() )
                 fp_angle = ( fp_angle.Invert() - ANGLE_180 ).Normalize();
 
             if( fp_angle != ANGLE_0 )
                 addAttribute( xformNode, "rotation", floatVal( fp_angle.AsDegrees(), 2 ) );
 
-            if( fp->GetLayer() != F_Cu )
+            if( fp->IsFlipped() )
                 addAttribute( xformNode,  "mirror", "true" );
         }