When construct libraries are purposely symlinked (as opposed of
collectively `npm install`ed), depending on how this is done they may
end up with multiple copies of `aws-cdk-lib`. If that happens, Aspects
from a different `aws-cdk-lib` copy than the one providing `App` will
not be applied.

The reason is the use of `Symbol('...')` instead of `Symbol.for('...')`
to keep the list of aspects on the construct object.

- The first version creates a unique symbol per library, while adding
  a naming hint.
- The second version deduplicates: all symbols with the same naming
  hint will receive the same symbol.

The second version is necessary to make sure that different copies
of the `aws-cdk-lib` library store their aspects under the same key.

Fixes #18921, #18778, #19390.