correctly deal with concatenated values in annotation attributes

[martinlippert]

Extracting string values from annotation attributes should take concatenated strings into account, incl. constants.

Examples are:

• @Component bean names, @Bean names
• @RequestMapping path extraction
• and probably many more

Code around this needs to be refactored to avoid code duplication as well.

[martinlippert]

Closing this item for the upcoming 4.29.0 release with all the work that has gone into this. Work on this continues for the 4.30.0 release via #1486