renderOneLine should render to one line

[glguy]

Previously the implementation was using layoutCompat with the hope that this operation rendered to a single line. It doesn't. This function is only used in the obscure :dumptests command where rendering to a single line is important for the file format.

[glguy]

I don't know how to test this easily with our current test framework. It improves the formatting of random output, so simple gold testing isn't going to cut it.

[RyanGlScott]

It improves the formatting of random output, so simple gold testing isn't going to cut it.

Will the random output be deterministic if you call :set-seed beforehand?

[glguy]

Link issue #1314