Add chars limit parameter for MojDecimal parser

:Release Notes:

:Detailed Notes:
Added parameter to specify maximum length of string to parse by
MojDecmal.
MojJsonParser passes MojString which already contains size. The only
place where we have no length of string is tests.

:Testing Performed:
test_core 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: I94de91ba77f33b083baddb80d9e51e4cf08ff36b
Reviewed-on: https://g2g.palm.com/3223
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>