Messages refactor

[Shatur]

The PR contains only renames. Decided to submit it first to simplify the future relations PR.

• Rename into Updates and Mutations. Shorter and these components aren't messages. We actually create messages from them.
• Use shorter methods in Mutations. Things like mutations.add_mutated_entity looks too redundant.
• In Updates I made few names more explicit since it accumulates not only changes.
• Use the variable name changes when referring to ChangeRanges.

[codecov]

Codecov Report

Attention: Patch coverage is 78.12500% with 14 lines in your changes missing coverage. Please review.

Project coverage is 79.86%. Comparing base (0a7e2a1) to head (0a420f2).
Report is 2 commits behind head on bevy-0.16-dev.

Files with missing lines	Patch %	Lines
src/server.rs	53.84%	12 Missing ⚠️
src/server/replication_messages/mutations.rs	92.30%	2 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           bevy-0.16-dev     #471      +/-   ##
=================================================
- Coverage          79.87%   79.86%   -0.02%     
=================================================
  Files                 52       52              
  Lines               2768     2766       -2     
=================================================
- Hits                2211     2209       -2     
  Misses               557      557              

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