support dots for unary operators (#20249)

* support dots for unary operators (closes #14161)
* docs for unary dot operators
* work around #20249

Author: stevengj

docs/src/index.md

@@ -135,7 +135,9 @@ to perform `^` element-by-element on arrays. For example,
 `[1,2,3] ^ 3` is not defined, since there is no standard
 mathematical meaning to "cubing" an array, but `[1,2,3] .^ 3`
 is defined as computing the elementwise
-(or "vectorized") result `[1^3, 2^3, 3^3]`.
+(or "vectorized") result `[1^3, 2^3, 3^3]`.  Similarly for unary
+operators like `!` or `√`, there is a corresponding `.√` that
+applies the operator elementwise.
 
 ```jldoctest
 julia> [1,2,3] .^ 3