abbr: expand command abbrs after decorators (#10396)

Currently, we expand command-abbrs (those with `--position command`) after `if`, but not after `command` or `builtin` or `time`:

```fish
abbr --add gc "git checkout"
```

will expand as `if gc` but not as `command gc`.

This was explicitly tested, but I have no idea why it shouldn't be?

src/reader.rs

@@ -4340,7 +4340,7 @@ fn expand_replacer(
     ))
 }
 
-// Extract all the token ranges in \p str, along with whether they are an undecorated command.
+// Extract all the token ranges in \p str, along with whether they are a command.
 // Tokens containing command substitutions are skipped; this ensures tokens are non-overlapping.
 struct PositionedToken {
     range: SourceRange,
@@ -4353,12 +4353,12 @@ fn extract_tokens(s: &wstr) -> Vec<PositionedToken> {
         | ParseTreeFlags::LEAVE_UNTERMINATED;
     let ast = Ast::parse(s, ast_flags, None);
 
-    // Helper to check if a node is the command portion of an undecorated statement.
+    // Helper to check if a node is the command portion of a decorated statement.
     let is_command = |node: &dyn ast::Node| {
         let mut cursor = Some(node);
         while let Some(cur) = cursor {
             if let Some(stmt) = cur.as_decorated_statement() {
-                if stmt.opt_decoration.is_none() && node.pointer_eq(&stmt.command) {
+                if node.pointer_eq(&stmt.command) {
                     return true;
                 }
             }

src/tests/abbrs.rs

@@ -131,8 +131,8 @@ fn test_abbreviations() {
     // Others should not be.
     validate!("of gc", None);
 
-    // Others should not be.
-    validate!("command gc", None);
+    // Other decorations generally should be.
+    validate!("command gc", None, "command git checkout");
 
     // yin/yang expands everywhere.
     validate!("command yin", None, "command yang");