Refactor Value cell path functions to fix bugs (#11066)

# Description
Slightly refactors the cell path functions (`insert_data_at_cell_path`,
etc.) for `Value` to fix a few bugs and ensure consistent behavior.
Namely, case (in)sensitivity now applies to lazy records just like it
does for regular `Records`. Also, the insert behavior of `insert` and
`upsert` now match, alongside fixing a few related bugs described below.
Otherwise, a few places were changed to use the `Record` API.

# Tests
Added tests for two bugs:
- `{a: {}} | insert a.b.c 0`: before this PR, doesn't create the
innermost record `c`.
- `{table: [[col]; [{a: 1}], [{a: 1}]]} | insert table.col.b 2`: before
this PR, doesn't add the field `b: 2` to each row.

crates/nu-command/tests/commands/insert.rs

@@ -87,3 +87,17 @@ fn lazy_record_test_values() {
     );
     assert_eq!(actual.out, "3");
 }
+
+#[test]
+fn deep_cell_path_creates_all_nested_records() {
+    let actual = nu!(r#"{a: {}} | insert a.b.c 0 | get a.b.c"#);
+    assert_eq!(actual.out, "0");
+}
+
+#[test]
+fn inserts_all_rows_in_table_in_record() {
+    let actual = nu!(
+        r#"{table: [[col]; [{a: 1}], [{a: 1}]]} | insert table.col.b 2 | get table.col.b | to nuon"#
+    );
+    assert_eq!(actual.out, "[2, 2]");
+}

crates/nu-command/tests/commands/upsert.rs

@@ -90,3 +90,17 @@ fn upsert_support_lazy_record() {
         nu!(r#"let x = (lazy make -c ["h"] -g {|a| $a | str upcase}); $x | upsert aa 10 | get aa"#);
     assert_eq!(actual.out, "10");
 }
+
+#[test]
+fn deep_cell_path_creates_all_nested_records() {
+    let actual = nu!(r#"{a: {}} | insert a.b.c 0 | get a.b.c"#);
+    assert_eq!(actual.out, "0");
+}
+
+#[test]
+fn upserts_all_rows_in_table_in_record() {
+    let actual = nu!(
+        r#"{table: [[col]; [{a: 1}], [{a: 1}]]} | insert table.col.b 2 | get table.col.b | to nuon"#
+    );
+    assert_eq!(actual.out, "[2, 2]");
+}