HHH-19610 make GraphParser support subTypeSubGraph

[Asanio06]

Today, Jpa's NamedEntityGraph annotation supports the use of subclassSubgraphs to define graphs linked to the subtypes of an Entity. It is also possible, via the entityManager, to do the same thing via the addTreatedSubgraph function.

The goal of this ticket is to improve GraphParser so that it supports a syntax that does the same thing. In this way, Hibernate's own NamedEntityGraph annotation will have 100% of the same functionality as Jpa’s.

I suggest the following syntax for defining a subclassSubgraphs:

(GraphParsingTestSubEntity:sub), name, description

Here we have a sub-graph specific to the GraphParsingTestSubEntity type, which is a sub-type of GraphParsingTestEntity.

The ticket related to my proposal: https://hibernate.atlassian.net/browse/HHH-19610

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https://hibernate.atlassian.net/browse/HHH-19610

[sebersole]

Hi @Asanio06, thanks for the PR!

Overall it's a good feature to add :)

I'm not a fan of using parenthesis here though - those are already used for sub-graphs so it introduces a bit of syntatic ambiguity. Sure, the use of the colon disambiguites it, but it also does so on its own:

GraphParsingTestSubEntity:sub, name, description

Bacause otherwise, something like this just looks odd -

(GraphParsingTestSubEntity:sub(subName, subOtherStuff)), name, description

whereas this is a little bit better:

GraphParsingTestSubEntity:sub(subName, subOtherStuff), name, description

[sebersole]

See also discussion at #hibernate-orm-dev > HHH-19610 Make GraphParser support subTypeSubGraph