fix: properly handle name conflicts in WDL documents.

[peterhuene]

The WDL spec requires that names within a document's "namespace" be unique.

Previously, tasks would check for conflicting workflow names, workflows would check for conflicting task names, and custom types would check for conflicting custom type names.

With this fix, it is now an error to define a task or workflow that conflicts with a custom type name and vice versa.

Update a few incorrect tests to show the new error.

Fixes #507.

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[peterhuene]

@a-frantz if we want to fix the name in workflows first, I'll revert the update to the gauntlet baseline.

[a-frantz]

@a-frantz if we want to fix the name in workflows first, I'll revert the update to the gauntlet baseline.

stjudecloud/workflows#292