add samples for bigDecimalExpectations of api-fluent

[robstoll]

Code related feature

See for the initial request: #624

With this issue we want to add samples for bigDecimalExpectations.kt of api-fluent

Following the things you need to do:

api-fluent

• add one function per non-deprecated function in bigDecimalExpectations.kt to BigDecimalExpectationSamples (see BigDecimalExpectationSamples)
• refer to the sample in the KDoc of the corresponding function in bigDecimalExpectations via @sample (check out toEqual in anyExpectations.kt to see how you have to refer to the sample)

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[timacosta]

I'll work on this. I've been just checking similar issues and PRs related to it so feel free to assign it to me if there is no issue.

[timacosta]

@robstoll PR #988 for this. Feel free to comment in the PR if it needs to be extended or if any explanatory comment is necessary.