Fix usage of --tabs flag while converting to json (#12115) (#12251)

closes #12115 

# Description
This fix addresses a bug where the --tabs flag couldn't be utilized due
to improper handling of the tab quantity provided by the user.
Previously, the code mistakenly attempted to convert the tab quantity to
a boolean value, leading to a conversion error. The resolution involves
adjusting the condition clauses to properly validate the presence of the
flag's value. Now, the code checks whether the get_flag() function
returns a value or None associated with the --tabs flag. This adjustment
enables the --tabs flag to function correctly, triggering the
appropriate condition and allowing the conversion to proceed as
expected. Similarly, the fix applies to the --indent flag. Additionally,
a default case was added, and the conversion now works properly without
flags. Two tests were added to validate the corrected behavior of these
flags.

# User-Facing Changes
Now the conversion should work properly instead of displaying an error.

# Tests + Formatting
-🟢 toolkit fmt
-🟢 toolkit clippy
-🟢 toolkit test
-🟢 toolkit test stdlib

To run added tests:
- cargo test --package nu-command --test main --
format_conversions::json::test_tabs_indent_flag
- cargo test --package nu-command --test main --
format_conversions::json::test_indent_flag

crates/nu-command/src/formats/to/json.rs

@@ -45,7 +45,8 @@ impl Command for ToJson {
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let raw = call.has_flag(engine_state, stack, "raw")?;
-        let use_tabs = call.has_flag(engine_state, stack, "tabs")?;
+        let use_tabs = call.get_flag(engine_state, stack, "tabs")?;
+        let indent = call.get_flag(engine_state, stack, "indent")?;
 
         let span = call.head;
         // allow ranges to expand and turn into array
@@ -55,12 +56,12 @@ impl Command for ToJson {
 
         let json_result = if raw {
             nu_json::to_string_raw(&json_value)
-        } else if use_tabs {
-            let tab_count: usize = call.get_flag(engine_state, stack, "tabs")?.unwrap_or(1);
+        } else if let Some(tab_count) = use_tabs {
             nu_json::to_string_with_tab_indentation(&json_value, tab_count)
-        } else {
-            let indent: usize = call.get_flag(engine_state, stack, "indent")?.unwrap_or(2);
+        } else if let Some(indent) = indent {
             nu_json::to_string_with_indent(&json_value, indent)
+        } else {
+            nu_json::to_string(&json_value)
         };
 
         match json_result {