Anchor API rework

[metalgearsloth]

Previously:

• Anchored anchored on the spot (or at least attempted to) but was not ECS
• AnchorEntity would always run anchoring even if the entity was already anchored.

Now:

• AnchorEntity has overloads to move the entity and then anchor it.
• AnchorEntity does not double-anchor and cause hellbugs if it's the same tile.
• Reanchor got purged because I'd rather just explicitly unanchor and re-anchor to simplify content even though we take a performance hit.
• Tests for all of the above.

I wouild've obsoleted reanchor but the issue is we'd have to raise the anchor changes in lieu of it which would almost certainly need to double-handling on content. Most forks are likely only using the anchor state change events anyway.

Content PR is Space-Wizards-Federation/space-station-14#129