Prepend indent for user-provided multi-line compilation messages

[yevhenii-nadtochii]

This PR updates Compilation object, so that it prints multi-line error and warning messages, indenting each following line (after the first) with the length of the leading prefix.

An example of a real compilation error from validation using this version of ProtoData:

> Task :java-tests:validating:launchTestFixturesProtoData FAILED
e: file:///Users/yevhenii/Projects/Spine/validation-master/java-tests/validating/src/testFixtures/proto/spine/test/tools/validate/numbers.proto:39:5: The `(range)` option could not parse the passed range value.
   Value: `[5.0 .. +1.0]`.
   Target field: `spine.test.tools.validate.Probability.value`.
   Reason: the lower bound `5.0` must be less than the upper bound `1.0`.
   Examples of the correct ranges: `(-5..5]`, `[0 .. 10)`.

Concatenation for String expressions

Additionally, this PR moves operators for String expression concatenation introduced in validation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.95%. Comparing base (f6be09a) to head (07d99eb).
Report is 10 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #353      +/-   ##
============================================
+ Coverage     73.85%   73.95%   +0.09%     
- Complexity      613      618       +5     
============================================
  Files           197      198       +1     
  Lines          4296     4311      +15     
  Branches        397      398       +1     
============================================
+ Hits           3173     3188      +15     
  Misses          996      996              
  Partials        127      127              

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[yevhenii-nadtochii]

@armiol @alexander-yevsyukov PTAL

[alexander-yevsyukov]

LGTM