[libc][complex] implement different flavors of `creal` and `cimag` functions (#113300)

I have commented out the test for `neg_zero`(creal) because :

1. real(neg_zero + 0.0i) equals zero.
2. re

[libc][complex] implement different flavors of `creal` and `cimag` functions (#113300)

I have commented out the test for `neg_zero`(creal) because :

1. real(neg_zero + 0.0i) equals zero.
2. real(neg_zero - 0.0i) equals neg_zero.

I am not sure if this is the intended behaviour.

[EDIT]
I have updated tests for `neg_zero` (creal) to be :

```
EXPECT_FP_EQ(func(CFPT(neg_zero - zero * 1.0i)), neg_zero);
EXPECT_FP_EQ(func(CFPT(neg_zero + zero * 1.0i)), zero);
```

because all three [gcc, clang and GNU MPC] also give the same result.
https://godbolt.org/z/hxhcn6aof
and it seems that it is indeed the correct behaviour since Imaginary
types are not supported yet, refer #113671

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