Allow open to work with 'from ...' block commands (#5049)

* Remove panic from BlockCommands run function

Instead of panicing, the run method now returns an error to prevent
nushell from unexpected termination.

* Add ability to open command to run with blocks

The open command tries to parse the content of the file
if there is a command called 'from (file ending)'.  This works
fine if the command was 'built in' because the run method doesn't
fail in this case.  It did fail on a BlockCommand, though.

This change will first probe if the command contains a block and
evaluate it, if this is the case.  If there is no block, it will run
the command the same way as before.

* Add test open files with BlockCommands

* Update open.rs

* Adjust file type on open with BlockCommand parser

Co-authored-by: JT <547158+jntrnr@users.noreply.github.com>

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

@@ -260,3 +260,20 @@ fn open_dir_is_ls() {
         assert_eq!(actual.out, "3");
     })
 }
+
+#[test]
+fn test_open_block_command() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats",
+        r#"
+            def "from blockcommandparser" [] { lines | split column ",|," }
+            let values = (open sample.blockcommandparser)
+            echo ($values | get column1 | get 0)
+            echo ($values | get column2 | get 0)
+            echo ($values | get column1 | get 1)
+            echo ($values | get column2 | get 1)
+        "#
+    );
+
+    assert_eq!(actual.out, "abcd")
+}