www/{*chromium,iridium}: unbreak build with icu 73

[rnagy]

Summary

As of icu 73 C++ nullptr, char16_t, override, final and noexcept are used
instead of defines. These definitions can be removed when the bundled icu
gets updated to 73. For more details, see:
https://unicode-org.atlassian.net/browse/ICU-21833 and
https://github.com/unicode-org/icu/commit/28643799377ecf654564f6f31854b02788cebe33

Fixes 270817

[rene]

In the commit log, can you prefix the PR number with "PR: " so that the commit is logged in the PR?

[dhw]

After applying the patch to my ports tree (at main-n615777-7e591c4f2380), my poudriere-devel package-builder was able to build www/chromium successfully; the resulting package installed on my laptop and appears to run as usual.

[rnagy]

commited as f5487f8d23309891b6faacaa9eb517f97ece429d