test: Add a new --quiet flag to suppress output

The --quiet flag is useful when only the exit status matters.

Fix the documentation for the -t flag to no longer claim that `type` can
print "keyword", as it never does that.

Stop printing a blank line for functions/builtins when the -p flag has
been passed. It's just not useful.
Adopt the new type -q flag in the other functions
type: Stop claiming `grep` is a function

Use `functions -q` instead of searching the `functiosn -na` list for the
provided word. This may result in an automatically-loaded function being
sourced, but that happens anyway with the default output.

This change means the results of `test -q foo` can be relied upon to
indicate whether `foo` can actually be invoked. Previosly, if `foo` was
the name of an automatically-loaded function file but did not actually
define a function `foo`, and there was no execuable `foo`, then `type -q
foo` would lie and say `foo` can be invoked when it can't.