Move detail header floating_conversion.hpp to detail subdirectory

[davidwendt]

Description

Moves the 'cudf/fixed_point/floating_conversion.hpp' to cudf/fixed_point/detail/ subdirectory since it only contains declarations and definition in the detail namespace.
It had previously been its own module. https://docs.rapids.ai/api/libcudf/stable/modules.html

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[ttnghia]

FYI: This will break spark-rapids-jni build as the header is used in https://github.com/NVIDIA/spark-rapids-jni/blob/7ee7b1c20fd473b6b976f4d36bbfeaaebcc29aaf/src/main/cpp/src/decimal_utils.cu#L24.

[davidwendt]

FYI: This will break spark-rapids-jni build as the header is used in https://github.com/NVIDIA/spark-rapids-jni/blob/7ee7b1c20fd473b6b976f4d36bbfeaaebcc29aaf/src/main/cpp/src/decimal_utils.cu#L24.

I will mark this breaking for this. Perhaps you could put a PR up in spark-rapids?
The file should not have been in the public API directory since it only has detail functions in it.

[davidwendt]

/merge