Relax Pure::Parser's comment regex to allow any characters in a multi-line comment

[sjahu]

The regex used by Pure::Parser for ignoring comments in JSON tries to do some fancy handling to prohibit nested comments, but it causes it to choke on strings that would otherwise be legit (i.e. that can be parsed by Ext::Parser or by a C compiler).

For example, a couple strings that are parsed correctly by Ext::Parser but not Pure::Parser:

This is the original regex (visualized by Regexper):

This is the simplified regex after my changes (Regexper):

I added a test to assert that a comment containing /* is parseable. Note that the test case immediately above that change asserts that a nested ANSI C-style comment still triggers an exception.

[sjahu]

(CI hasn't run because "First-time contributors need a maintainer to approve running workflows.")