Introduce tests for @Priority declared on stereotypes.

[manovotn]

Fixes #282

Tests are taken from Weld PR here - weld/core#2559
I also added one extra test (testSeveralPrioritiesInSingleStereotypeHierarchy) that works with several declarations of @Priority in a hierarchy of single stereotype. We don't explicitly define this in spec text, but it is implied by annotation inheritance and overriding.

[Ladicek]

Otherwise looking good.

[manovotn]

Incorporated javadoc suggestions, the only remaining questionmark is #311 (comment)

[Ladicek]

Just to repeat it here: maybe add a test or two with an @Inherited stereotype? :-)

[manovotn]

Just to repeat it here: maybe add a test or two with an @Inherited stereotype? :-)

True, we could add at least a simple test to see if the working case (single `@Priority) is inherited properly.
Quickly scanning TCKs, I can see we test this for scopes declared on stereotypes, but that's about it. But maybe I am just not seeing it.

[manovotn]

@Ladicek I have added requested tests, do you think we need any further changes?

[manovotn]

@Ladicek this PR now reflects the changes made to specification and tests for definition exception if a single stereotype indirectly declares more than one priority value. I think we are good to go now.

[Ladicek]

Otherwise LGTM.