Actors v8

[arajasek]

This is in support of FIP-0031. Although the FIP replaces the primary usecases of this repo with WASM actors, this change is still needed to support:

• the migration
• Go-based state reads

This PR:

• Bumps the version and code CIDs
  • Note that the synthetic code CIDs are expected to be replaced by content addressed CIDs
• Introduces the simple migration needed to migrate code CIDs

[anorth]

deleting the actors themselves (except the state objects)

@Stebalien whoah hold up, can we talk about this please? I understand why you say that, but I think there are better alternatives. cc @ZenGround0

@Kubuxu after this lands you probably wanna rebase your FIP work onto v8.

[anorth]

Introduces the simple migration needed to migrate code CIDs

Consider doing this in a separate PR to keep this one purely mechanical. I didn't notice the new code when scanning.

[codecov-commenter]

Codecov Report

Merging #1576 (1059f01) into master (b1d4451) will not change coverage. The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master   #1576   +/-   ##
======================================
  Coverage    69.0%   69.0%           
======================================
  Files          72      72           
  Lines        8791    8791           
======================================
  Hits         6072    6072           
  Misses       1858    1858           
  Partials      861     861