allow current day to be highlighted (#11954)

# Description

This PR tweaks the built-in `cal` command so that it's still nushell-y
but looks closer to the "expected" cal by abbreviating the name of the
days. I also added the ability to color the current day with the current
"header" color.

### Before

![image](https://github.com/nushell/nushell/assets/343840/c7ad3017-d872-4d39-926d-cc99b097d934)

### After

![image](https://github.com/nushell/nushell/assets/343840/735c4f2e-9867-4cd7-ae3b-397dd02059d7)



# User-Facing Changes
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crates/nu-command/tests/commands/cal.rs

@@ -4,7 +4,8 @@ use nu_test_support::{nu, pipeline};
 fn cal_full_year() {
     let actual = nu!("cal -y --full-year 2010 | first | to json -r");
 
-    let first_week_2010_json = r#"{"year": 2010,"sunday": null,"monday": null,"tuesday": null,"wednesday": null,"thursday": null,"friday": 1,"saturday": 2}"#;
+    let first_week_2010_json =
+        r#"{"year": 2010,"su": null,"mo": null,"tu": null,"we": null,"th": null,"fr": 1,"sa": 2}"#;
 
     assert_eq!(actual.out, first_week_2010_json);
 }
@@ -17,16 +18,16 @@ fn cal_february_2020_leap_year() {
         "#
     ));
 
-    let cal_february_json = r#"[{"year": 2020,"month": "february","sunday": null,"monday": null,"tuesday": null,"wednesday": null,"thursday": null,"friday": null,"saturday": 1},{"year": 2020,"month": "february","sunday": 2,"monday": 3,"tuesday": 4,"wednesday": 5,"thursday": 6,"friday": 7,"saturday": 8},{"year": 2020,"month": "february","sunday": 9,"monday": 10,"tuesday": 11,"wednesday": 12,"thursday": 13,"friday": 14,"saturday": 15},{"year": 2020,"month": "february","sunday": 16,"monday": 17,"tuesday": 18,"wednesday": 19,"thursday": 20,"friday": 21,"saturday": 22},{"year": 2020,"month": "february","sunday": 23,"monday": 24,"tuesday": 25,"wednesday": 26,"thursday": 27,"friday": 28,"saturday": 29}]"#;
+    let cal_february_json = r#"[{"year": 2020,"month": "february","su": null,"mo": null,"tu": null,"we": null,"th": null,"fr": null,"sa": 1},{"year": 2020,"month": "february","su": 2,"mo": 3,"tu": 4,"we": 5,"th": 6,"fr": 7,"sa": 8},{"year": 2020,"month": "february","su": 9,"mo": 10,"tu": 11,"we": 12,"th": 13,"fr": 14,"sa": 15},{"year": 2020,"month": "february","su": 16,"mo": 17,"tu": 18,"we": 19,"th": 20,"fr": 21,"sa": 22},{"year": 2020,"month": "february","su": 23,"mo": 24,"tu": 25,"we": 26,"th": 27,"fr": 28,"sa": 29}]"#;
 
     assert_eq!(actual.out, cal_february_json);
 }
 
 #[test]
-fn cal_friday_the_thirteenths_in_2015() {
+fn cal_fr_the_thirteenths_in_2015() {
     let actual = nu!(pipeline(
         r#"
-        cal --full-year 2015 | default 0 friday | where friday == 13 | length
+        cal --full-year 2015 | default 0 fr | where fr == 13 | length
         "#
     ));
 
@@ -45,14 +46,14 @@ fn cal_rows_in_2020() {
 }
 
 #[test]
-fn cal_week_day_start_monday() {
+fn cal_week_day_start_mo() {
     let actual = nu!(pipeline(
         r#"
-        cal --full-year 2020 -m --month-names --week-start monday | where month == january | to json -r
+        cal --full-year 2020 -m --month-names --week-start mo | where month == january | to json -r
         "#
     ));
 
-    let cal_january_json = r#"[{"month": "january","monday": null,"tuesday": null,"wednesday": 1,"thursday": 2,"friday": 3,"saturday": 4,"sunday": 5},{"month": "january","monday": 6,"tuesday": 7,"wednesday": 8,"thursday": 9,"friday": 10,"saturday": 11,"sunday": 12},{"month": "january","monday": 13,"tuesday": 14,"wednesday": 15,"thursday": 16,"friday": 17,"saturday": 18,"sunday": 19},{"month": "january","monday": 20,"tuesday": 21,"wednesday": 22,"thursday": 23,"friday": 24,"saturday": 25,"sunday": 26},{"month": "january","monday": 27,"tuesday": 28,"wednesday": 29,"thursday": 30,"friday": 31,"saturday": null,"sunday": null}]"#;
+    let cal_january_json = r#"[{"month": "january","mo": null,"tu": null,"we": 1,"th": 2,"fr": 3,"sa": 4,"su": 5},{"month": "january","mo": 6,"tu": 7,"we": 8,"th": 9,"fr": 10,"sa": 11,"su": 12},{"month": "january","mo": 13,"tu": 14,"we": 15,"th": 16,"fr": 17,"sa": 18,"su": 19},{"month": "january","mo": 20,"tu": 21,"we": 22,"th": 23,"fr": 24,"sa": 25,"su": 26},{"month": "january","mo": 27,"tu": 28,"we": 29,"th": 30,"fr": 31,"sa": null,"su": null}]"#;
 
     assert_eq!(actual.out, cal_january_json);
 }
@@ -61,7 +62,7 @@ fn cal_week_day_start_monday() {
 fn cal_sees_pipeline_year() {
     let actual = nu!(pipeline(
         r#"
-        cal --full-year 1020 | get monday | first 4 | to json -r
+        cal --full-year 1020 | get mo | first 4 | to json -r
         "#
     ));