Deprecation: #69863 - Deprecate getTemplateVariableContainer function 

See forge#69863

Description 

RenderingContext->getTemplateVariableContainer has been marked as deprecated in favor of getVariableProvider due to a changed concept for variable provisioning in standalone fluid. It now does more than just contain variables so a change in naming is necessary.

Impact 

Calling this method directly will trigger a deprecation log entry.

Affected Installations 

Any TYPO3 instance using getTemplateVariableContainer method directly within an extension or third-party code.

Migration 

Use getVariableProvider instead of getTemplateVariableContainer.