Unify metrics DataPoints collection

[fraillt]

Problem

At the moment there's zero code reuse in DataPoints collection phase. Due to too much copy/paste there are few issues:

• there are inefficiencies by doing unnecessary .clone()
• I noticed at least one bug in PrecomputedSum::delta where no_attribute_tracker uses get_value instead of get_and_reset_value.
• hard to understand the core logic of aggregator, versus implementation details of how DataPoints are collected.
• makes very hard to experiment with performance improvements in measuring and/or collecting phase. E.g. if I change something within ValueMap, I need to go and update at minimum 5 aggregators (if we add ExpoHistogram) * 2 (delta/comulative) = 10 places.
• makes very hard to review, because simple change will affect at least 10 places.

Solution

Hide implementation details of ValueMap, and provide simple collect_cumulative and collect_delta functions instead (similar idea as in #2114).
In the future we'll be able to experiment and improve ValueMap implementation and get benefits across all aggregators.

[cijothomas]

Agreed. In other implementations like OTel .NET, the entire logic of keeping track of metric points, look up, etc are done in a common place (i.e not repeated for each instument type).

Related:#1566