Refactor to support multiple parse errors (#8765)

# Description

This is a pretty heavy refactor of the parser to support multiple parser
errors. It has a few issues we should address before landing:

- [x] In some cases, error quality has gotten worse `1 / "bob"` for
example
- [x] if/else isn't currently parsing correctly
- probably others

# User-Facing Changes

This may have error quality degradation as we adjust to the new error
reporting mechanism.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass
- `cargo run -- crates/nu-utils/standard_library/tests.nu` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-cli/tests/completions.rs

@@ -663,8 +663,8 @@ fn run_external_completion(block: &str, input: &str) -> Vec<Suggestion> {
     let (dir, _, mut engine_state, mut stack) = new_engine();
     let (_, delta) = {
         let mut working_set = StateWorkingSet::new(&engine_state);
-        let (block, err) = parse(&mut working_set, None, block.as_bytes(), false, &[]);
-        assert!(err.is_none());
+        let block = parse(&mut working_set, None, block.as_bytes(), false, &[]);
+        assert!(working_set.parse_errors.is_empty());
 
         (block, working_set.render())
     };

crates/nu-cli/tests/support/completions_helpers.rs

@@ -146,9 +146,9 @@ pub fn merge_input(
     let (block, delta) = {
         let mut working_set = StateWorkingSet::new(engine_state);
 
-        let (block, err) = parse(&mut working_set, None, input, false, &[]);
+        let block = parse(&mut working_set, None, input, false, &[]);
 
-        assert!(err.is_none());
+        assert!(working_set.parse_errors.is_empty());
 
         (block, working_set.render())
     };