[Feat][C++] Output the error message when access value in Result fail

[acezen]

Proposed changes

current when access value fail with Result, it just output message like:
error attempting to access value from result containing error.

This change change the behavior that output the message of error it contain.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have added tests that prove my fix is effective or that my feature works
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Further comments

Fixed issue: #218

[CLAassistant]

All committers have signed the CLA.

[lixueclaire]

LGTM~