BREAKING: Use SIP-6 algorithm for state encryption

[Mrtenz]

Closes #944.

This changes the state encryption to use the algorithm as described in SIP-6 for deriving the encryption key. For this, I slightly refactored the deriveEntropy function to take a magic value as extra parameter, and created a new magic value for state encryption.

The encryption logic was moved to the snap_manageState JSON-RPC method.

Breaking changes

• This breaks existing state, as the encryption keys are now different.
• The API for the SnapController has changed: it no longer takes a getAppKey parameter.

[codecov-commenter]

Codecov Report

Merging #1055 (806c0ad) into main (1fe00c8) will increase coverage by 0.42%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1055      +/-   ##
==========================================
+ Coverage   94.13%   94.55%   +0.42%     
==========================================
  Files         132      130       -2     
  Lines        4348     4336      -12     
  Branches      735      734       -1     
==========================================
+ Hits         4093     4100       +7     
+ Misses        255      236      -19     

Impacted Files	Coverage Δ
packages/rpc-methods/src/__fixtures__/entropy.ts	100.00% <ø> (ø)
packages/rpc-methods/src/restricted/getEntropy.ts	100.00% <100.00%> (ø)
packages/rpc-methods/src/restricted/manageState.ts	94.73% <100.00%> (+2.00%)	⬆️
packages/rpc-methods/src/utils.ts	75.75% <100.00%> (+48.48%)	⬆️
...ages/snaps-controllers/src/snaps/SnapController.ts	95.07% <100.00%> (-0.13%)	⬇️
packages/snaps-utils/src/entropy.ts	100.00% <100.00%> (ø)
packages/snaps-utils/src/manifest/validation.ts	100.00% <100.00%> (ø)
packages/rpc-methods/src/__fixtures__/index.ts
packages/rpc-methods/src/permitted/index.ts
packages/rpc-methods/src/restricted/index.ts

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