Fix italic and underline ANSI escape codes

[kamilkrzywanski]

Fixes #4105.

AnsiEscape was missing italic (SGR 3) and had underline mapped to 3 instead of 4. After the Jansi removal, that made italic warn as invalid and underline render as italic.

Changes

• Add ITALIC("3") and correct UNDERLINE to "4"
• Document italic in the pattern layout style keywords
• Add regression tests with hard-coded SGR sequences
• Changelog entry

Checklist

• Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise
• ./mvnw verify passed
• Non-trivial changes contain an entry file in the src/changelog/.2.x.x directory
• Tests are provided

[ramanathan1504]

@kamilkrzywanski, thanks! I'll try to get this cleared whenever I find the time. Thanks for your patience.

[ramanathan1504]

Can u extend the test case for remaining format also?

[ramanathan1504]

not needed remove the comments

[ramanathan1504]

here also remove comments

[ramanathan1504]

On the issue, @vy suspected AnsiEscape should also be "checked for other differences" against Jansi — that part is still open. Worth doing the full sweep: walk every constant in org.fusesource.jansi.AnsiRenderer.Code (the enum JAnsiTextRenderer.toCode used before #3070) and check it resolves in AnsiEscape. italic isn't the only casualty — try faint or blink_slow and you'll see the pattern. A quick way to check a candidate: AnsiEscape.createSequence(name) returning a bare ESC[m means the name didn't resolve, so the style silently does nothing and you get a The style attribute X is incorrect. warning on the StatusLogger.

[kamilkrzywanski]

@ramanathan1504 thanks for the review.

Did the full Jansi AnsiRenderer.Code sweep and added the missing names (faint, blink_slow, etc.). Extended the tests and removed those comments.

Should be ready for another look.

[ramanathan1504]

@kamilkrzywanski

1. pattern-layout.adoc picked up only part of the new list — intensity_bold, intensity_faint, negative_on/negative_off, conceal_on/conceal_off, underline_off, blink_off and bg_default all work but aren't in the keyword list. add them, or say the list isn't exhaustive?
2. when AnsiEscapeTest fails it prints expected: <> but was: <> — the escape chars are invisible. could you pass the style name as the assertion message, the way JAnsiTextRendererTest shows them as hex? and while you're in there, the @CsvSource covers 22 of the 43 names, the rest are free.
3. main still has UNDERLINE("3") and no ITALIC — would you do the port too? no changelog entry there, the 2.x one covers both.