exp(pi*i) produces slightly incorrect result

Basically, exp(pi*i) where i is the imaginary unit should produce -1 but produces a slightly different
result with Boost 1.77.0; however it produces the correct result with Boost 1.74.0. The following program reproduces the issue:
```
#include

using CT = boost::multiprecision::cpp_complex_50;
static const auto pi = boost::math::constants::pi();
static const auto i = CT(0, 1);

int main() {
std::cout << exp(pi*i) << std::endl;
// Output when compiled with Boost 1.74.0 is -1 as expected.
// Output when compiled with Boost 1.77.0 is (-1,4.33483e-51).
// Note: The equivalent program using std::complex when run in compiler
// explorer produces a similar result: (-1,1.22465e-16). Don't know if this
// could be related.
// Note 2: My version of g++ under which this was compiled is 11.2.0.
}
```

Start with the standalone reproducer using boost/multiprecision/cpp_complex.hpp and compare its output under Boost 1.74.0 and 1.77.0. Investigate the exp(pi*i) path and determine whether the regression can be addressed; done means the reported discrepancy is resolved and the expected output is confirmed.

Written by the indexing model from the issue text.