Extend tests of bcmath extension (#11563)

Add coverage for:

* different formats of zero (0, 0.0)
* small integers and decimals
* large integers and large decimals with la

Extend tests of bcmath extension (#11563)

Add coverage for:

* different formats of zero (0, 0.0)
* small integers and decimals
* large integers and large decimals with large fractional part
* negative numbers for all of the above ones

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