implementing case-sensitive & case-insensitive completion matching (#2556)

Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>

crates/nu-cli/src/completion/matchers/case_sensitive.rs

@@ -0,0 +1,28 @@
+use crate::completion::matchers;
+
+pub struct Matcher;
+
+impl matchers::Matcher for Matcher {
+    fn matches(&self, partial: &str, from: &str) -> bool {
+        from.starts_with(partial)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn completes_case_sensitive() {
+        let matcher: Box<dyn matchers::Matcher> = Box::new(Matcher);
+
+        //Should match
+        assert!(matcher.matches("shouldmatch", "shouldmatch"));
+        assert!(matcher.matches("shouldm", "shouldmatch"));
+        assert!(matcher.matches("--also-should-m", "--also-should-match"));
+        assert!(matcher.matches("-also-should-m", "-also-should-match"));
+
+        // Should not match
+        assert!(!matcher.matches("--Shouldnot", "--shouldnotmatch"));
+    }
+}