add step_sqrt_signed

[EmilHvitfeldt]

In much the same way step_log() has a signed argument, I think step_sqrt() should as well. A signed sqrt() would uphold the ordering of near-zero values better then what signed log would do

values <- c(-3 ^ seq(5, -3, by = -0.1), 0, 3 ^ seq(-3, 5, by = 0.1))

plot(values)

plot(sign(values) * log(abs(values)))

plot(sign(values) * sqrt(abs(values)))

^{Created on 2022-03-26 by the reprex package (v2.0.1)}