Improve completions for exact matches (Issue #14794) (#15387)

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Fixes #14794.
# Description
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# User-Facing Changes
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Makes it so that (even if) the command ends in a slash, exact matches
are still preferred over partial matches.
For example, `foo/bar/as` -> `foo/bar/asdf` but not `foo/bars/asdf`.
# Tests + Formatting
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---------

Co-authored-by: Yash Thakur <45539777+ysthakur@users.noreply.github.com>

crates/nu-cli/src/completions/completion_common.rs

@@ -98,7 +98,7 @@ fn complete_rec(
                 }
 
                 // For https://github.com/nushell/nushell/issues/13204
-                if isdir && options.match_algorithm == MatchAlgorithm::Prefix {
+                if options.match_algorithm == MatchAlgorithm::Prefix {
                     let exact_match = if options.case_sensitive {
                         entry_name.eq(base)
                     } else {

crates/nu-cli/tests/completions/mod.rs

@@ -2224,6 +2224,16 @@ fn exact_match() {
         &vec![file(dir.join("partial").join("hello.txt")).as_str()],
         &suggestions,
     );
+
+    let target_dir = format!("open {}", file(dir.join("partial").join("hello"))); // No trailing slash
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Despite no trailing slash, since it's an exact match, only 'partial/hello.txt' should be suggested, not
+    // 'partial-a/hello' and stuff. See issue #14794 for details.
+    match_suggestions(
+        &vec![file(dir.join("partial").join("hello.txt")).as_str()],
+        &suggestions,
+    );
 }
 
 #[ignore = "was reverted, still needs fixing"]