Clarify validation of getter methods in the spec document

This issue arose in the context of JIRA issue https://issues.jboss.org/browse/WFLY-11956 "@PostConstruct on @ApplicationScoped bean called too late in case @Valid is annotated on a business method". The discussion includes comments from Gunnar Morling and Guillaume Smet from the Hibernate Validator project and also from Santiago Pericas-Geertsen, and the conclusion was that the discussion of getters in the spec isn't quite right.

Start by reading the referenced WFLY-11956 JIRA discussion and the current specification text about getter methods. Identify the passage described as inaccurate and revise it to reflect the discussion's conclusion; done means the spec wording is technically agreed and the relevant documentation change is reviewed.

Written by the indexing model from the issue text.