Report error for task.hash/task.workDir in process script section

[bentsherman]

Summary

The implicit task variable in a process exposes properties such as task.hash and task.workDir that depend on the task hash, which in turn is derived from the process script. Using these properties in the script: (or stub:) section therefore creates a circular dependency.

This PR adds a rule in TypeCheckingVisitorEx that reports a type error for each use of task.hash or task.workDir in the script and stub sections.

Details

• A new TaskScriptPropertyVisitor inner class walks the script/stub body and flags any PropertyExpression whose property is hash/workDir and whose receiver resolves to TaskConfig (so detection is type-based, not just name-based).
• The check runs on both script:/shell: (node.exec when node.type != "exec") and stub: (node.stub).
• The exec: section is exempt, since it does not contribute to the command hash in the same way.

Tests

Added cases to TypeCheckingTest:

• error reported for task.hash and task.workDir in the script: section
• error reported for task.hash and task.workDir in the stub: section
• other task properties (task.cpus, task.process, task.attempt) are still allowed
• task.hash/task.workDir are allowed in the exec: section

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