Introduce DecimalTest in gtest_mojocore

:Release Notes:
gtest_mojocore have now DecimalTest test-suite based on MojDecimalTest
with additional tests that exposes current issues with MojDecimal

:Detailed Notes:
- exposed issue with rounding while converting from double
  (ctor_double, ctor_double_with_rounding, floatValue_reconvert)
- exposed issue with rounding during parsing number
  (parse_with_rounding)
- exposed issue with parsing numbers where mantissa re-aligned with
  exponent (parse_unbalanced_small, number_parser_unbalanced_big)
- exposed issue with hiding fact of overflow
  (parse_overflow_mantissa, parse_overflow_exponent,
  parse_overflow_exponent_bound)

:Testing Performed:
MojDecimalTest and gtest_mojocore

:QA Notes:

:Issues Addressed:
[GF-36958] MojDecimal in DB8 have issues with rounding and exponent

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: I01e2078c6fc19223b62381379af86ee2582df72c
Reviewed-on: https://g2g.palm.com/3259
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>