Audit Public Sniff Properties

## What problem would the enhancement address for VIP?

There are 47 instances of public properties within sniff classes. Public properties allow changing sniff behaviour by customising a ruleset by passing different types of values via the ruleset. VIP [uses](https://github.com/Automattic/VIP-Coding-Standards/blob/918b0ca0fe986ae58babd77c7ab5e0ff7a6f7eb5/.phpcs.xml.dist#L29) itself to adjust how a WPCS sniff runs.

However, I suspect that some of the instances are NOT meant to be changed - whitelisted Batcache params, restricted constant names and declarations, etc.

## Describe the solution you'd like

Audit the uses and convert to `private` where suitable. Document the rest on a [wiki page](https://github.com/Automattic/VIP-Coding-Standards/wiki/Custom-properties-for-VIPCS-Sniffs).

I'll create a linked list of the 47 instances, possibly along with who added them, to check if they are meant to be public or not.

For those that are meant to be changeable, then a better approach for some cases is to have a private default list of values, and then a public custom list, and the two lists merged together - that way, the custom rulesets don't need to also add in the default values as well.

## Additional context
Note that this would technically be a breaking change, since it is possible that someone was already making use of these unintentional public properties in their own rulesets. As such, this would require a bump from `0.y.z` to `0.y+1.0`, or a normal major release if `1.0.0` has been released in the meantime.

Review the 47 public properties in the sniff classes, starting with the VIP override in .phpcs.xml.dist and the linked list of instances when available. For each property, determine whether it is intended to be configurable or private, and record the configurable-property guidance on the Custom properties for VIPCS Sniffs wiki page. Done means suitable properties are private, remaining properties are documented, and the breaking-change release impact is addressed.

Written by the indexing model from the issue text.