Fix#3093. PR #2595 added the ability for Xlsx Reader to accept a custom color palette. With no examples other than the one at hand, which included a full complement of 64 colors, that PR required 64 colors in the palette. It turns out that Mac Numbers exports to Excel with a palette with less than 64 colors. So, with an example of that at hand, relax the original restriction and accept a palette of any size.
Fix#2499, which see for details of an obscure problem affecting both PhpSpreadsheet and Excel. Add support for palette contained in workbook styles. This seems to be a very rare occurrence, so allow it only when the palette contains exactly 64 entries. If there are other possibilities, we'll presumably have a new workbook to guide us how to handle them. Also add some tests for specification of indexed color without palette, another rarity (no in-range examples amongst our current files). Also change one private static array, initialized once at run-time and never changed, to a constant.
oleibman