vBuild() method in message builders

[dmdashenkov]

This PR introduces the io.spine.protobuf.ValidatingBuilder interface—the substitution for the old io.spine.validate.ValidatingBuilder. The new interface is implemented directly in the generated message builders.

The correct way to use message builders now is:

• use vBuild() method in most cases; it builds the message and performs validation;
• to avoid validation, use buildPartial();
• usage of build() is discoureged.

The old UseVBuilders ErrorProne check is now disabled, as it is not recommended to use VBuilders anymore. Instead, we introduce the UseVBuild check, which makes sure users avoid calling build().

[codecov]

Codecov Report

Merging #409 into master will increase coverage by 0.75%.
The diff coverage is 68.09%.

@@             Coverage Diff             @@
##             master    #409      +/-   ##
===========================================
+ Coverage     81.34%   82.1%   +0.75%     
- Complexity     2732    2769      +37     
===========================================
  Files           429     432       +3     
  Lines         10407   10451      +44     
  Branches        610     619       +9     
===========================================
+ Hits           8466    8581     +115     
+ Misses         1759    1684      -75     
- Partials        182     186       +4

[dmdashenkov]

@alexander-yevsyukov, PTAL.

[alexander-yevsyukov]

Please address coverage as we discussed vocally.

[dmdashenkov]

@alexander-yevsyukov, PTAL again.

[alexander-yevsyukov]

LGTM, with one small request.

[alexander-yevsyukov]

Please document the package.