2022-May-02 - Prerelease - 2.6.731

Refactor code for querying unit tech for players. (#10394)

* Refactor code for querying unit tech for players.

This change makes TechTracker an actual instance class on GameData and cleans up the APIs to retrieve tech information from UnitAttachment.

This is a pure code re-organizing change, no functional changes.

Besides improving the API, this should pave way for allowing the TechTracker to cache this information and only update it when tech changes, which should speed up the engine quite a bit - since very basic things like getting unit attack / defense / movement requires expensive tech look up operations currently (which shows up in profiles).