Add winget upgrades command (#1179)

`winget upgrade` has two modes:

* No parameters (at all) lists available upgrades
* Any parameter attempts to match and upgrade a package

Much like `winget list`, `winget upgrade` prints a spinner, then a
table, and then additionally a footer.

The `winget list` completions handle output through `detect columns
--guess` and return structured data.

Presumably because `detect columns --guess` does not work on `winget
upgrade`, no output handling was done until now.

1. Split off trimLoadingSymbol as a common function between two, now
three, commands
2. Implement a separate command `winget upgrades` instead of handling
`winget upgrade` because of overloaded behavior complicating
implementation

Now, `winget upgrades` can be used to get structured data of available
upgrades, while `winget upgrade` behaves like before, without parameters
has text output, and with parameters upgrades packages.

While introducing a separate command is not strictly completions [for
external commands], this one is very close to the completions, logic,
and use cases. Keeping it close will help discovery and future
development which may integrate returning structured data into the
"normal" completions.

---

I was not able to test for “no updates” output.

---

```nushell
winget upgrades
# => ╭───┬──────────────────────────────────┬─────────────────────┬───────────────────────────────┬───────────────────────────────┬────────╮
# => │ # │               name               │         id          │            version            │           available           │ source │
# => ├───┼──────────────────────────────────┼─────────────────────┼───────────────────────────────┼───────────────────────────────┼────────┤
# => │ 0 │ Go Programming Language amd64 g… │ GoLang.Go           │ 1.25.1                        │ 1.25.2                        │ winget │
# => ╰───┴──────────────────────────────────┴─────────────────────┴───────────────────────────────┴───────────────────────────────┴────────╯
```

Author: Kissaki

custom-completions/winget/winget-completions.nu

@@ -36,6 +36,10 @@ def "nu-complete winget flagify" [name: string, value: any, --short(-s)] {
   }
 }
 
+def "nu-complete winget trimLoadingSymbol" [] {
+    str replace -r r#'^[^\w]*'# ""
+}
+
 def "nu-complete winget uninstall package id" [] {
     ^winget export -s winget -o __winget-temp__.json | ignore
     let results = (open __winget-temp__.json | get Sources.Packages | first | get PackageIdentifier)
@@ -259,8 +263,7 @@ export def "winget search" [
         )
 
     let output = ^winget ...$params
-        # remove loading symbols at start of output
-        | str replace -r r#'^[^\w]*'# ""
+        | nu-complete winget trimLoadingSymbol
     if $raw or $help {
         $output
     } else {
@@ -319,8 +322,7 @@ export def "winget list" [
     )
 
     let output = ^winget ...$params
-    # remove loading symbols at start of output
-    | str replace -r r#'^[^\w]*'# ""
+    | nu-complete winget trimLoadingSymbol
     if $help or $raw {
         $output
     } else {
@@ -338,6 +340,35 @@ export def "winget list" [
 }
 export alias "winget ls" = winget list
 
+def "winget upgrades" [] {
+    let output = ^winget upgrade | nu-complete winget trimLoadingSymbol
+    
+    # Do nothing when no upgrades available
+    if ( ($output | str starts-with 'No') or ($output | str starts-with '0') ) { return }
+    
+    let lines = $output | lines
+    let head = $lines | first
+    let rest = $lines | skip 2
+    
+    let colnames = [ Name Id Version Available Source ]
+    # We must be unicode aware in determining and using index; winget uses `…` elippses to hide overflow
+    let cols = $colnames | each {|col| $head | {name: $col i: ($head | str index-of $col --grapheme-clusters) } }
+    
+    let dirty = $rest | each {|line|
+        let chars = $line | split chars
+        {
+            name:      ( $chars | slice ($cols.0.i)..($cols.1.i - 1) | str join | str trim )
+            id:        ( $chars | slice ($cols.1.i)..($cols.2.i - 1) | str join | str trim )
+            version:   ( $chars | slice ($cols.2.i)..($cols.3.i - 1) | str join | str trim )
+            available: ( $chars | slice ($cols.3.i)..($cols.4.i - 1) | str join | str trim )
+            source:    ( $chars | slice ($cols.4.i).. | str join | str trim )
+        }
+    }
+    # Reject footer lines, in a best effort approach, because there is no clear separator or definitely identifiable form change.
+    # We expect `x upgrades available.` to follow the table. Then maybe `x package(s) have version numbers that cannot be determined. Use --include-unknown to see all results.`
+    return ($dirty | take until {|x| $x.source == '' })
+}
+
 # Upgrades the given package
 export extern "winget upgrade" [
     query?: string,