LDEV-1697 tighten dotted cfc resolution + contextual throw with source CFC/property

[zspitzer]

https://luceeserver.atlassian.net/browse/LDEV-1697

• Drop the silent simple-name getCFC(name) fallback in SessionFactoryData.getEntityByCFCName (both 2-arg and 3-arg variants). A dotted reference like cfc="ns.Name" now requires the matching /ns mapping in the current app — previously a registered Name entity in any namespace would resolve, iteration-order-dependent (passed Windows, failed Linux).
• HBMCreator.setForeignEntityName now uses the non-throwing 3-arg variant and throws contextual on null: Cannot resolve entity reference [ns.Name] on property [foo] of [...]. Names the source CFC + property so the misconfiguration is immediately diagnosable.
• Spec rewritten as two variants: (1) parent app without the /childns mapping correctly throws with the contextual message; (2) parent declaring the mapping (via url.withMapping=true) resolves and entityNew succeeds.

Matches ACF behaviour (ACF already throws this scenario per the LDEV-1697 tracker doc).