This updates the in-code docs on the trig functions to line up with the
docs, removes the docs, and uses the now mostly identical generated
docs. This means we only need to document these functions in one place -
right next to the code.
This modifies the ESQL test infrastructure to generate more of the
documentation for functions. It generates the *Description* section, the
*Examples* section, and the *Parameters* section as separate files so we
can use them as needed. It also generates a `layout` file that's just
a guess as to how to render the whole thing. In some cases it'll work
and we can use that instead of hand maintaining a "top level"
description file for the function.
Most newly generated files are unused. We have to chose to pick them up
by replacing the sections we were manually maintaining with an include
of the generated section. Or by replacing the entire hand maintained
file with the generated top level file.
Relates to #104247
