[BEAM-13015, #21250] Remove looking up thread local metrics container holder and object creation on hot path

[lukecwik]

This got rid of about half of the overhead of activating the metrics container for the current thread.

The updated implementation is about 48 ms for the two calls to activate:

While the existing implementation is 75 ms (+8 ms not shown for the Closeable#close invocation):

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[lukecwik]

R: @steveniemitz

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Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[steveniemitz]

sorry I was OOO last week, I'll take a look at this today!

[lukecwik]

No, worries. Hopefully you had a good vacation.

[steveniemitz]

No, worries. Hopefully you had a good vacation.

I did, thank you!

this looks good to me, always great to get rid of static state as well.