All document scores are positive 32-bit floating point numbers. However, this
wasn't previously documented.
This can result in surprising behavior, such as precision loss, for users when
customizing scores using the function score query.
This commit updates an existing admonition in the function score query docs to
document the 32-bits precision limit. It also updates the search API reference
docs to note that `_score` is a 32-bit float.
03600e4e12