The kind of template entity a diagnostic targets - the singular form of the
top-level section the entity is declared in. Every documented section has a
variant; the ones whose children are addressable by logical ID (resources,
parameters, outputs, mappings, conditions, rules, and metadata keys) are
the ones diagnostics attribute findings to today.
Splits a section-absolute, slash-separated template path (such as
Parameters/MyParam/Type or Outputs/MyOutput/Value) into the entity type
of the section’s children and the logical ID of the entity it addresses.
Returns None for paths that are not rooted at a documented top-level
section - resource-relative dotted paths like Properties.BucketName - or
that name a section with no child segment.