Increase test coverage for isclose() function with edge cases for special complex numbers

In Lib/test/test_cmath.py, the isclose() function misses certain test cases for special complex numbers with infinity and Nan. As docs tell:

-inf, inf and NaN behave similarly to the IEEE 754 Standard. 
That is, NaN is not close to anything, even itself. 
inf and -inf are only close to themselves. 

This applies for complex numbers as well (inf + infj , -inf - infj and NaN + NaNj behave in the same way).

Linked PRs

• gh-149923
• gh-149948
• gh-150938

从 Lib/test/test_cmath.py 开始，检查现有的 isclose() 测试以及文档中说明的 infinity、negative infinity 和 NaN 的行为。为所述的特殊复数情况添加覆盖，然后运行 cmath 测试文件以确认预期结果。