Allow lowercase letters for array tool pin numbering

The ARRAY_AXIS class now accepts lowercase letters (a-z) as input for
alphabetic numbering schemes and preserves that case in the output.
This allows users to create pin numbers like a1, b1, c1 which are
commonly used in DIN 41612 and other backplane connectors.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/22787

common/array_axis.cpp

@@ -37,7 +37,11 @@ static bool schemeNonUnitColsStartAt0( ARRAY_AXIS::NUMBERING_TYPE type )
 }
 
 
-ARRAY_AXIS::ARRAY_AXIS() : m_type( NUMBERING_TYPE::NUMBERING_NUMERIC ), m_offset( 0 ), m_step( 1 )
+ARRAY_AXIS::ARRAY_AXIS() :
+        m_type( NUMBERING_TYPE::NUMBERING_NUMERIC ),
+        m_offset( 0 ),
+        m_step( 1 ),
+        m_useLowercase( false )
 {
 }
 
@@ -76,7 +80,14 @@ std::optional<int> ARRAY_AXIS::getNumberingOffset( const wxString& str ) const
 
     for( unsigned i = 0; i < str.length(); i++ )
     {
-        int chIndex = alphabet.Find( str[i], false );
+        wxUniChar ch = str[i];
+
+        // For alphabetic types, convert to uppercase for lookup since our alphabets
+        // are defined with uppercase letters. This allows users to enter lowercase.
+        if( !TypeIsNumeric( m_type ) && ch >= 'a' && ch <= 'z' )
+            ch = ch - 'a' + 'A';
+
+        int chIndex = alphabet.Find( ch, false );
 
         if( chIndex == wxNOT_FOUND )
             return std::optional<int>{};
@@ -109,6 +120,18 @@ bool ARRAY_AXIS::SetOffset( const wxString& aOffsetName )
     if( !offset )
         return false;
 
+    // For alphabetic types, check if the user entered lowercase letters.
+    // If so, we'll output lowercase letters as well.
+    if( !TypeIsNumeric( m_type ) && !aOffsetName.IsEmpty() )
+    {
+        wxUniChar firstChar = aOffsetName[0];
+        m_useLowercase = ( firstChar >= 'a' && firstChar <= 'z' );
+    }
+    else
+    {
+        m_useLowercase = false;
+    }
+
     SetOffset( *offset );
     return true;
 }
@@ -139,5 +162,11 @@ wxString ARRAY_AXIS::GetItemNumber( int n ) const
 
     n = m_offset + m_step * n;
 
-    return AlphabeticFromIndex( n, alphabet, nonUnitColsStartAt0 );
+    wxString result = AlphabeticFromIndex( n, alphabet, nonUnitColsStartAt0 );
+
+    // If the user entered a lowercase starting value, output lowercase letters
+    if( m_useLowercase )
+        result = result.Lower();
+
+    return result;
 }