[MDEP-562] Auto-select dependency tree tokens for capable consoles

[wilx]

This is a draft because the implementation seems way too involved for choosing tree branch characters. There should be a better way for Maven to give plugins information about its logging output capabilities, particularly the effective encoding and whether logging targets a console or a file. A supported Maven API for this would be preferable to making each plugin inspect logger implementations, stream identity and optional terminal-library versions.

Fixes #997 (MDEP-562).

Behavior

When tokens is omitted, text trees use the existing extended box-drawing tokens if Maven is logging to an interactive terminal whose output encoding can represent all four branch characters. This supports UTF-8 and compatible legacy encodings such as CP437 and CP850. Detection reads Maven's existing JLine or Jansi metadata without installing a terminal, changing console settings or adding runtime dependencies.

Explicit -Dtokens=standard|extended|whitespace settings take precedence and bypass detection. Automatic selection keeps ASCII for outputFile, -l/--log-file, batch mode, redirected output, dumb terminals and unavailable or ambiguous metadata. Forced color does not override those checks. Other output formats are unchanged, and the Java 8 / Maven 3.6.3 minimum remains unchanged.

Why this remains a draft

Maven 3.6.3's Jansi does not expose sufficient public metadata, so automatic selection remains ASCII there. Maven 4 also retains that fallback: both current 4.0.x and 4.1.x/master expose the JLine terminal but do not expose the active logging destination through a plugin-accessible API. A terminal can be present while the logger writes to a -l file. The logger has a package-private logSink and a public setter, but no getter; the CLI selects the actual writer separately. The implementation avoids inspecting private fields.

This limitation is documented in ConsoleSupport and the goal documentation. Explicit extended tokens still work on those Maven versions. The draft is intended to support discussion of a Maven-level capability API and whether this amount of plugin-side detection is appropriate.

Validation

• Regression tests were written and observed failing before the corresponding implementation changes.
• mvn clean verify -Prun-its: all 103 integration builds passed.
• After the final runtime changes, mvn verify -Prun-its '-Dinvoker.test=tree*': 465 unit tests, zero failures/errors, one existing skip; all nine tree integration builds passed.
• Linux pseudo-terminal and redirected-output checks covered Maven 3.6.3 / Java 8, Maven 3.8.8 / Java 8, Maven 3.9.16 / Java 17 and 21, Maven 3.10.0-rc-1 / Java 21, and Maven 4.0.0-rc-6 / Java 21. Checks included explicit styles, batch mode, -l, forced color, separate stdout/stderr, and ASCII / CP437 / CP850 encodings. The final artifact passed all 20 final runtime checks.
• Maven 4.0.x and 4.1.x/master were additionally inspected at 9a2aa9b036 and a98d8fa111; the relevant logger implementation is identical. These branch tips were not runtime-tested.
• mvn spotless:apply spotless:check and git diff --check passed. The subsequent class Javadoc note changes no runtime behavior.
• Native Windows and macOS console behavior has not been exercised.

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