Many objects fit into the contextual data that needs to be passed between
caller/callee whether they are part of the application code or between
application and library. The current state is that frameworks such Spring
define many "holder" classes which give access to the underlying object
stored in a ThreadLocal (e.g. LocaleContextHolder). But could this be part
of the JDK itself?
I wish to write the following code:
```
Locale locale = Locale.VALUE.get()
...
I also wish to avoid propagating the value every time:
```
getTranslation("key", locale)
```
If every framework has a different scopedvalue we are no better than where
we started.
Should every class define an instance of its ScopedValue as a field? or
should we have a generic holder keyed by the Class object itself? Or should
it be part of the ScopedValue API itself?
```
ScopedValue.get(Locale.class)
ScopedValue.where(Locale.class, Locale.ENGLISH)
```
needless to say, for the highest payoff, this needs to be part of java.base.
