string match needs option to print entire line matching the pattern

[krader1961]

So I was converting a bunch of __fish_sgrep uses and noticed that the equivalent string match only prints the portion of the line matching the pattern. That is, string match default behavior is equivalent to __fish_sgrep -o (i.e., grep -o). Rather than forcing people to prefix and append extra wildcard characters so the entire string/line is printed it would be nice if there was a flag to request the entire string (or line) be printed.

See also issue #3956 which I mistakenly opened thinking the default behavior is what I'm requesting here due to an unrelated problem in converting a use of __fish_sgrep.

[krader1961]

FWIW, this should probably be done via a --filter / -f flag for consistency with the proposed fix for issue #3348.

[krader1961]

I am going to implement similar logic for string replace --filter in the next few days to resolve issue #3348. Both changes will make using the string command in fish 2.6.0 "friendlier".