Use Increment to contain amount to be incremented

What does this MR do and why?

Introduce an Increment struct to contain a counter increment amount and a ref.

In this MR, all existing increment amounts are moved into the amount.

ref will be used in a subsequent MR. !104216 (merged)

This MR is extracted from !104216 (merged) to make it easier to review.

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Related to #373469