Add new tests for Math built-ins

test/built-ins/Math/Log2/Log2-basicTests.js

test/built-ins/Math/Log2/Log2-descriptor.js

test/built-ins/Math/Log2/Log2-length.js

test/built-ins/Math/acosh/acosh-descriptor.js

test/built-ins/Math/acosh/acosh-length.js

test/built-ins/Math/acosh/acosh-specialVals.js

test/built-ins/Math/asinh/asinh-descriptor.js

test/built-ins/Math/asinh/asinh-length.js

test/built-ins/Math/asinh/asinh-specialVals.js

test/built-ins/Math/atanh/atanh-descriptor.js

test/built-ins/Math/atanh/atanh-length.js

test/built-ins/Math/atanh/atanh-specialVals.js

test/built-ins/Math/cbrt/cbrt-descriptor.js

test/built-ins/Math/cbrt/cbrt-length.js

test/built-ins/Math/cbrt/cbrt-specialValues.js

test/built-ins/Math/cosh/cosh-descriptor.js

test/built-ins/Math/cosh/cosh-length.js

test/built-ins/Math/cosh/cosh-specialVals.js

test/built-ins/Math/expm1/expm1-descriptor.js

test/built-ins/Math/expm1/expm1-length.js