Add setTabColor Method to Set Worksheet Tab Colors

[HergenD]

Problem:

Users cannot currently set the tab color of worksheets using the extension. Setting tab colors is a valuable feature for organizing and visually distinguishing worksheets within a workbook, enhancing user experience and productivity.

Solution:

This pull request adds the setTabColor method to the Excel class, enabling users to set the color of the current worksheet's tab. The method leverages the worksheet_set_tab_color function from libxlsxwriter to apply the specified color.

Changes Made:

• Added setTabColor Method:
  • Implemented setTabColor in excel.c, which accepts a color parameter corresponding to predefined color constants.
• Registered Color Constants:
  • Added color constants (e.g., COLOR_RED, COLOR_BLUE) to the Excel class for easy reference in PHP code.
• Updated Method Entries:
  • Included the new method in the xls_methods[] array for integration into the extension.
• Added Test Case:
  • Created set_tab_color.phpt to test setting the tab color and ensure the method functions correctly.
  • The test confirms that the tab color is applied without errors and the Excel file is generated properly.