[REF] Convert Custom Field BAO Class to use standard Civi:: rather than local static vars

[seamuslee001]

Overview

This converts the Custom Field BAO class to using the standard Civi::$statics functionality rather than using local static vars

Before

Local static vars used

After

Civi::$statics functionality used

Technical Details

currently also incorporates #16613 but will rebase once that is merged in

Comments

ping @eileenmcnaughton @mattwire

[civibot]

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[mattwire]

@seamuslee001 Not sure if others agree but for this kind of cleanup I find it easier to just have one PR and 2 or 3 commits (like you've done). As it's quite easy to review each commit and see that the changes are similar.

[colemanw]

Retest this please

[eileenmcnaughton]

@seamuslee001 this generally makes sense but you haven't sold it to jenkins

[eileenmcnaughton]

stale - closing for now