[TASK] Rename method getName of TypoScriptConstants VH

The name "getName" will be reserved in Fluid 3.0 and is
ambiguous. This patch renames that method to become
"getFieldName" which is less ambiguous and conflict free.

Additionally the ViewHelper is changed so it no longer
accesses deprecated property AbstractViewHelper->
viewHelperVariableContainer, instead accessing the
ViewHelperVariableContainer via $this->renderingContext.

Resolves: #89861
Releases: master
Change-Id: Iea474625917293afe67326f765c6a77f7fbe9b73
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62541


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>