Fix #9337 — recognize compact -T<n> and --threads=<n> Maven flags

[xerno]

NetBeans only detected the spaced forms (-T 2, --threads 2) as parallel builds. The compact forms (-T2) and GNU-style equals form (--threads=2) were not recognized, so for multi-module projects NetBeans kept its output tree-folding active and crashed with an NPE in CommandLineOutputHandler.trimTree when concurrent module events arrived (Cannot read field "type" because "start" is null).

Extracts a threadsArgValue() helper that recognizes all four forms and uses it from both isMultiThreadedMaven and isMultiThreadedMvnd.

Side effects, both intentional improvements

• mvnd: compact -T1 now correctly flips to single-threaded mode (previously only the spaced -T 1 did).
• A non-numeric suffix after -T (e.g. -Tfoo) is now reported as the threads value verbatim; Maven itself rejects such input.

Tests

Added cases for -T2, -T10, -T1C, -T1, --threads=2, --threads=1, and a dangling -T to both MavenCommandParametersAnalyzerTest and MavenDaemonCommandParametersAnalyzerTest.

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