[paulbalandan]

Description
Our colour detection came from composer/xdebug-handler, which has since dropped it. Terminal::hasColorSupport() now follows Symfony's StreamOutput::hasColorSupport(), keeping one difference: a TTY on Unix gets colour whatever its TERM, where Symfony requires TERM to match its pattern.

The checks run in this order:

1. NO_COLOR turns colour off.
2. FORCE_COLOR turns it on, even when the output is piped.
3. A stream that is not a TTY gets no colour, except under MSYS2's MINGW32 and MINGW64.
4. On Windows, VT100 support turns colour on.
5. TERM_PROGRAM=Hyper, COLORTERM, ANSICON or ConEmuANSI=ON turns it on.
6. TERM=dumb turns it off.
7. Otherwise, colour is on, except that Windows also needs TERM to match Symfony's pattern (xterm*, cygwin*, *-256color and similar).

The variables are read through env(), so they can also be set in .env. NO_COLOR and FORCE_COLOR count only when they are not empty, whatever the value, as no-color.org and force-color.org specify.

Behaviour changes, listed in the changelog:

• An empty NO_COLOR no longer turns colour off.
• TERM=dumb turns colour off.
• On Windows, a stream that is not a TTY no longer gets colour from ANSICON, ConEmu or TERM.
• On Windows without VT100 support, more TERM values now get colour, where previously only xterm did.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide