Fix try not working with let, etc. (#13885)

# Description
Partialy addresses #13868. `try` does not catch non-zero exit code
errors from the last command in a pipeline if the result is assigned to
a variable using `let` (or `mut`).

This was fixed by adding a new `OutDest::Value` case. This is used when
the pipeline is in a "value" position. I.e., it will be collected into a
value. This ended up replacing most of the usages of `OutDest::Capture`.
So, this PR also renames `OutDest::Capture` to `OutDest::PipeSeparate`
to better fit the few remaining use cases for it.

# User-Facing Changes
Bug fix.

# Tests + Formatting
Added two tests.

crates/nu-engine/src/compile/call.rs

@@ -108,7 +108,7 @@ pub(crate) fn compile_call(
                     working_set,
                     builder,
                     expr,
-                    RedirectModes::capture_out(arg.span()),
+                    RedirectModes::value(arg.span()),
                     None,
                     arg_reg,
                 )?;