Move custom-completion auto-generate scripts to needs-update (#1076)

A user in Discord recently tried to run the auto-generate script to
create completions from `<command> --help` and had issues. In examining
the scripts, I found that they used `build-string`, which was deprecated
and removed over 2 years ago. In order to prevent future confusion until
(and if) these files are updated, I'm moving them to a `needs-update`
directory in the repo.

Any other outdated files can be moved there as well.

needs-update/custom-completions/auto-generate/parse-help.nu

@@ -0,0 +1,79 @@
+
+
+# parses a input string in --help format and returns a table of parsed flags
+def parse-help [] {
+    # help format  '        -s,                      --long                   <format>                 description   '
+    $in | parse -r '\s\s+(?:-(?P<short>\w)[,\s]+)?(?:--(?P<long>[\w-]+))\s*(?:<(?P<format>.*)>)?\s*(?P<description>.*)?'
+}
+
+# takes a table of parsed help commands in format [short? long format? description]
+def make-completion [command_name: string] {
+    build-string "extern \"" $command_name "\" [\n" ($in | each { |it|
+        build-string "\t--" $it.long (if ($it.short | is-empty) == false {
+            build-string "(-" $it.short ")"
+        }) (if ($it.description | is-empty) == false {
+            build-string "\t\t# " $it.description
+        })
+    } | str join "\n") "\n\t...args\n]"
+}
+
+module tests {
+    def test-cargo [] {
+        let expect = [
+            [short long format description];
+            [V version '' 'Print version info and exit']
+            ['' list '' 'List installed commands']
+            ['' explain 'CODE' 'Run `rustc --explain CODE`']
+            [v verbose '' 'Use verbose output (-vv very verbose/build.rs output)']
+            [q quiet '' 'Do not print cargo log messages']
+            ['' color 'WHEN' 'Coloring: auto, always, never']
+            ['' frozen '' 'Require Cargo.lock and cache are up to date']
+            ['' locked '' 'Require Cargo.lock is up to date']
+            ['' offline '' 'Run without accessing the network']
+            ['' config 'KEY=VALUE' 'Override a configuration value (unstable)']
+            [h help '' 'Print help information']
+    ]
+
+        let result = (cargo --help | parse-help)
+
+        if $result == $expect {
+            "passed"
+        } else {
+            $result
+        }
+    }
+
+    def test-nu [] {
+        let expect = [
+            [short long format description];
+            [h help '' 'Display this help message']
+            ['' stdin '' 'redirect the stdin']
+            [l login '' 'start as a login shell']
+            [i interactive '' 'start as an interactive shell']
+            [v version '' 'print the version']
+            [p perf '' 'start and print performance metrics during startup']
+            ['' testbin 'String' 'run internal test binary']
+            [c commands 'String' 'run the given commands and then exit']
+            ['' config 'String' 'start with an alternate config file']
+            ['' env-config 'String' 'start with an alternate environment config file']
+            ['' log-level 'String' 'log level for performance logs']
+            ['t' threads 'Int' 'threads to use for parallel commands']
+    ]
+
+        let result = (nu --help | parse-help)
+
+        if $result == $expect {
+            "passed"
+        } else {
+            $result
+        }
+    }
+
+    export def run-tests [] {
+        [
+            [test result];
+            ['cargo' (do { test-cargo })]
+            ['nu' (do { test-nu })]
+        ]
+    }
+}