Support php 8.0 printf() family changes for %h/%H/%.*

Parse them in PrintfCheckerPlugin and ConversionSpec. Emit compatibility warnings about support for versions before php 8.

  . printf() and friends now support the %h and %H format specifiers. These
    are the same as %g and %G, but always use "." as the decimal separator,
    rather than determining it through the LC_NUMERIC locale.
  . printf() and friends now support using "*" as width or precision, in which
    case the width/precision is passed as an argument to printf. This also
    allows using precision -1 with %g, %G, %h and %H. For example, the following
    code can be used to reproduce PHP's default floating point formatting:

        printf("%.*H", (int) ini_get("precision"), $float);
        printf("%.*H", (int) ini_get("serialize_precision"), $float);

Start by reading PrintfCheckerPlugin and ConversionSpec to trace how printf() format specifiers, width, and precision are parsed. Implement support for %h, %H, and * width or precision, then add compatibility warnings for PHP versions before 8.0; done means all listed forms are recognized and warnings are emitted where required.