Skip Java test matrices for documentation-only PRs

[vcolin7]

Description

• Adds a deny-first PR change classifier for the unified Java pull request pipeline.
• Suppresses Java test matrix generation only when every changed path has a known non-Java validation route.
• Keeps Swagger/AutoRest and TypeSpec inputs, source and test resources, version/dependency inputs, engineering files, mixed changes, and unknown paths on the normal test path.
• Keeps Build and Analyze enabled so their existing validation remains unchanged in this first rollout phase.
• Supports a definition-level ForceFullValidation=true rollback switch.
• Adds table-driven Pester coverage, including the real empty-matrix integration path.

Motivation

Documentation-only PRs currently select a fallback package and allocate test workers even though they cannot change Java behavior. Recent examples consumed 3–10 test workers and roughly 32–94 agent-minutes. This change removes only those test matrices while preserving the rest of PR validation.

Validation

• Pester 5.7.1: 29 tests passed in simulated Azure CI mode.
• Modified pipeline YAML parsed successfully.
• Local matrix integration produced {} for docs-only changes and populated matrices for functional changes.
• Docs-only test PR #50290, build 6762970: Build, Analyze, and matrix generation succeeded; 0 test jobs and 0 test workers.
• Functional test PR #50291, build 6762974: 10 test jobs were generated and workers allocated.
• Mixed test PR #50292, build 6762976: the functional path won; 10 test jobs were generated and workers allocated.

Scope

This is Phase 1 only. The additional classification outputs are diagnostic/reserved for later work to route focused validation and potentially gate Build or Analyze after their unique checks are relocated.

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).
35 pipeline(s) were filtered out due to trigger conditions.
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[Copilot]

Pull request overview

This PR introduces a deny-first PR change classifier to the unified Java PR pipeline so that documentation-only pull requests can avoid generating Java test matrices (and therefore avoid allocating test workers), while keeping Build and Analyze validation intact.

Changes:

• Adds eng/scripts/Classify-PRChanges.ps1 to classify changed paths and (when safe) clear job-local PackageInfo to force an empty {} test matrix.
• Wires the classifier into the PR matrix pre-generation path in eng/pipelines/templates/jobs/ci.yml.
• Adds table-driven Pester coverage in eng/scripts/tests/Classify-PRChanges.tests.ps1, including the “empty matrix integration” path.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
eng/scripts/tests/Classify-PRChanges.tests.ps1	Adds Pester tests validating docs-only vs functional classification and the matrix-emptying integration path.
eng/scripts/Classify-PRChanges.ps1	Implements deny-first path classification and the PackageInfo-clearing behavior used to suppress test matrix generation.
eng/pipelines/templates/jobs/ci.yml	Invokes the classifier during PR matrix pre-generation to suppress test matrices only for docs-only change sets.

Suppressed comments (1)

eng/scripts/tests/Classify-PRChanges.tests.ps1:36

• With the classifier no longer treating arbitrary cspell.* files as safe to skip tests, these paths should be in the "requires Java tests" set to preserve deny-first behavior (and to ensure sdk/cosmos/pipeline/** remains fully validated).

        @{ Path = 'sdk/example/example/src/test/resources/cspell.json' }

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