[ImportVerilog] Support %p format specifier for int, string, and struct

[VecoMr]

$display("%p", ...) and friends failed with "unsupported format specifier `%p`" for any argument, since the format-string parser's switch had no case for it.

%p (IEEE § 21.2.1.7) auto-formats its argument as a SystemVerilog assignment pattern: integers use the calling task's default radix, strings are quoted, and structs recurse field by field as '{name:value, ...}.

Limitation:

Enums, packed unions, %0p, arrays, classes, and dynamic collections are explicitly rejected with a clear diagnostic.

[circt-bot]

Results of circt-tests run for 905d6b9 compared to results for e1b33ef: no change to test results.

[fzi-hielscher]

They really went to town with the format specifiers in SV.

Is there a specific reason to not support arrays and maybe even enums and unions? Also, if I'm reading the LRM correctly, we could simply treat %p and %0p as the same.