As configured, Phpstan running under Php7 reports no errors. However, running under Php8, it reports 218 (!) errors. The vast majority of these are due to two reasons:
- renaming parameters in Php builtin functions in preparation for named parameters.
- using the new class `GdImage` rather than type `resource` as the argument type for many image-based functions.
Regardless of the cause, this will be a problem sooner or later. This PR is an attempt to get ahead of that problem. It tweaks only the Phpstan configuration files, without changing any PhpSpreadsheet code. Php7 continues to report no errors, and the number of errors for Php8 is reduced to 13. Although those 13 can also be tweaked, there is a case to be made that code corrections might be better in at least some of those instances. I will attend to those as one or more PRs after this one.
Because this involves no changes to code, and because Phpstan baseline is a common cause of merge difficulties, I will probably merge this in a day or two, more quickly than I customarily do.
oleibman