* Display aliases and custom commands in which; Fix#2810
Example output of nu after the commit is applied:
```shell
/home/leo/repos/nushell(feature/which_inspect_alias)> def docker-ps [] { docker ps --format '{{json .}}' | from json -o }
/home/leo/repos/nushell(feature/which_inspect_alias)> which docker-ps
───┬───────────┬────────────────────────┬─────────
# │ arg │ path │ builtin
───┼───────────┼────────────────────────┼─────────
0 │ docker-ps │ nushell custom command │ No
───┴───────────┴────────────────────────┴─────────
/home/leo/repos/nushell(feature/which_inspect_alias)> alias d = gid pd
/home/leo/repos/nushell(feature/which_inspect_alias)> which d
───┬─────┬───────────────┬─────────
# │ arg │ path │ builtin
───┼─────┼───────────────┼─────────
0 │ d │ nushell alias │ No
───┴─────┴───────────────┴─────────
```
* Update documentation
* Detect built-in commands passed as args to `which`
This expands the built-in `which` command to detect nushell commands
that may have the same name as a binary in the path.
* Allow which to interpret multiple arguments
Previously, it would discard any argument besides the first. This allows
`which` to process multiple arguments. It also makes the output a stream
of rows.
* Use map to build the output
* Add boolean column for builtins
* Use macros for entry creation shortcuts
* Process command args and use async_stream
In order to use `ichwh`, I'll need to use async_stream. But in order to
avoid lifetime errors with that, I have to process the command args
before using them. I'll admit I don't fully understand what is going on
with the `args.process(...)` function, but it works.
* Use `ichwh` for path searching
This commit transitions from `which` to `ichwh`. The path search is now
done asynchronously.
* Enable the `--all` flag on `which`
* Make `which` respect external commands
Escaped commands passed to wich (e.g., `which "^ls"`), are now searched
before builtins.
* Fix clippy warnings
This commit resolves two warnings from clippy, in light of #1142.
* Update Cargo.lock to get new `ichwh` version
`ichwh@0.2.1` has support for local paths.
* Add documentation for command
