Clean up existing VERIFY*() macros.

Chiefly:

• Remove unnecessary parentheses around variable names.
• Remove spaces between the type and variable in casts.
• Make the panic message for VERIFY0() reflect how the macro is used.
• Use %p to format pointers, except in Linux kernel code.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kay Pedersen <mail@mkwg.de>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Dag-Erling Smørgrav <des@FreeBSD.org>
Closes #15225