Add the newly-stablised features (try, extra_paired_delimiters) to the :5.40 feature bundle

[leonerd]

I didn't do this at first in #22123 because it seemed a bit more of a user-visible change. But discussing it today on the PSC call suggested it may still have merit.

Written here anyway, so we can discuss if it's a good idea or not.

[johannessen]

As a user, my mental model of feature bundles is that they generally enable all stable features of the given version of Perl. Anything else would surprise me.

So I think this is a good idea.

The impact on correctly-functioning programs is limited to those that have been loading the :5.39 or :5.40 feature bundle, which seems to imply that at most users of v5.39 are affected. How worried should we be about that?

[rwp0]

It is a good idea.

Even lesser boilerplates, and more focus on what matters.

The previous PR eliminated adding the experimental, and this one eliminates adding the feature pragma on top of the code (what matters) everytime.