Allow brick math 0.15 and 0.16

[BackEndTea]

0.15 removed the 'old' rounding mode constants, so this includes a BC layer in the BrickMathCalculator

Description

This MR allows installation of brick math versions 0.15 and 0.16.

0.14 changed the rounding mode to an enum, but kept backwards compatability. in 0.15 this BC layer was removed.

To support older brick/math versions (and older PHP versions), we introduce a BC layer in the BrickMathCalculator class.

Motivation and context

How has this been tested?

I have ran the phpunit tests with brick/math 0.14, 0.15 and 0.16.

Types of changes

• Bug fix (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 change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.

PHPUnit test are working for this MR, but there are some PHPStan failures. I'm not sure how to move forward with those.

[balu-lt]

After creating PR #634 for the 5.x branch, I noticed you had already opened this PR for the 4.x branch.

By the way, is there an ETA for the v5 release?