Fix#4629. Excel Xml can specify Conditional Formatting in 2 ways - either using a `conditionalFormatting` tag as a child of `worksheet`, or in a slightly different manner as a child of `worksheet->extLst`. Although these are both handled by PhpSpreadsheet, the former is lost if there exists a latter whose cell range (`sqref`) matches it. This PR merges the former with the latter in that circumstance, preserving both.
The issue also notes that `font` and `stopIfTrue` are not handled correctly. Support for those was missing in the `extlst` handling, and is now added with this PR.
oleibman