idn: add native AppleIDN (icucore) support for macOS/iOS

I implemented the IDN functions for macOS and iOS using Unicode
libraries coming with macOS and iOS.

Builds and runs her

idn: add native AppleIDN (icucore) support for macOS/iOS

I implemented the IDN functions for macOS and iOS using Unicode
libraries coming with macOS and iOS.

Builds and runs here on macOS 14.2.1. Also verified to load and
run on older macOS version 10.13.

Build requires macOS SDK 13 or equivalent.

Set `-DUSE_APPLE_IDN=ON` CMake option to enable it.
With autotools and other build tools, set these manual options:
```
CPPFLAGS=-DUSE_APPLE_IDN
LIBS=-licucore
```

Completes TODO 1.6.

TODO: add autotools option and feature-detection.

Refs: #5330 #5371
Co-authored-by: Viktor Szakats
Closes #13246

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idn: make Curl_idnconvert_hostname() use Curl_idn_decode()

In the name of less code duplication

Closes #13236

urlapi: return CURLUE_BAD_HOSTNAME if puny2idn encoding fails

And document it. Only return out of memory when it actually is a memory
problem.

Pointed-out-by: Jacob Mealey
C

urlapi: return CURLUE_BAD_HOSTNAME if puny2idn encoding fails

And document it. Only return out of memory when it actually is a memory
problem.

Pointed-out-by: Jacob Mealey
Closes #11674

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urlapi: CURLU_PUNY2IDN - convert from punycode to IDN name

Asssisted-by: Jay Satiro
Closes #11655

copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- save

copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING

checksrc is updated to allow non-year using copyright statements

Closes #10205

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urlapi: add CURLU_PUNYCODE

Allows curl_url_get() get the punycode version of host names for the
host name and URL parts.

Extend test 1560 to verify.

Closes #10109

idn: rename the files to idn.[ch] and hold all IDN functions

Closes #10094