As mentioned in #2900, something like
```fish
test -n "$var"; and set -l foo $var
```
is sufficiently idiomatic that it should be allowable.
Also fixes some additional weirdness with semicolons.
This removes semicolons at the end of the line and collapses
consecutive ones, while replacing meaningful semicolons with newlines.
I.e.
```fish
echo;
```
becomes
```fish
echo
```
but
```fish
echo; echo
```
becomes
```fish
echo
echo
```
Fixes#5859.
Fish keywords can be quoted and split across lines. Prior to this change
`fish_indent` would retain such odd, obfuscated, formatting. This change
results in all keywords being converted to their canonical form.
This required fixing a bug: the keyword member of parse_node_t wasn't being
populated. This hadn't been noticed prior to now because it wasn't used.
Fixes#2921
Modify `fish_indent` to emit redirections without a space before the target of
the redirection; e.g., "2>&1" rather than "2>& 1" as the former is clearer to
humans.
Fixes#2899
