add function to make env vars case-insensitive (#14390)

# Description

This PR adds a new function that allows one to get an env var
case-insensitively. I did this so we can hopefully stop having problems
when Windows has HKLM as path and HKCU as Path.

Instead of just changing every function that used the original one, I
chose the ones that I thought were specific to getting the path. I
didn't want to go all in and make every env get case insensitive, but
maybe we should? 🤷🏻‍♂️

closes #12676

# User-Facing Changes
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crates/nu-protocol/src/engine/engine_state.rs

@@ -14,6 +14,7 @@ use crate::{
 use fancy_regex::Regex;
 use lru::LruCache;
 use nu_path::AbsolutePathBuf;
+use nu_utils::IgnoreCaseExt;
 use std::{
     collections::HashMap,
     num::NonZeroUsize,
@@ -465,20 +466,12 @@ impl EngineState {
         None
     }
 
-    // Get the path environment variable in a platform agnostic way
-    pub fn get_path_env_var(&self) -> Option<&Value> {
-        let env_path_name_windows: &str = "Path";
-        let env_path_name_nix: &str = "PATH";
-
+    pub fn get_env_var_insensitive(&self, name: &str) -> Option<&Value> {
         for overlay_id in self.scope.active_overlays.iter().rev() {
             let overlay_name = String::from_utf8_lossy(self.get_overlay_name(*overlay_id));
             if let Some(env_vars) = self.env_vars.get(overlay_name.as_ref()) {
-                if let Some(val) = env_vars.get(env_path_name_nix) {
-                    return Some(val);
-                } else if let Some(val) = env_vars.get(env_path_name_windows) {
-                    return Some(val);
-                } else {
-                    return None;
+                if let Some(v) = env_vars.iter().find(|(k, _)| k.eq_ignore_case(name)) {
+                    return Some(v.1);
                 }
             }
         }

crates/nu-protocol/src/engine/stack.rs

@@ -5,6 +5,7 @@ use crate::{
     },
     Config, IntoValue, OutDest, ShellError, Span, Value, VarId, ENV_VARIABLE_ID, NU_VARIABLE_ID,
 };
+use nu_utils::IgnoreCaseExt;
 use std::{
     collections::{HashMap, HashSet},
     fs::File,
@@ -494,6 +495,40 @@ impl Stack {
         None
     }
 
+    // Case-Insensitive version of get_env_var
+    pub fn get_env_var_insensitive<'a>(
+        &'a self,
+        engine_state: &'a EngineState,
+        name: &str,
+    ) -> Option<&'a Value> {
+        for scope in self.env_vars.iter().rev() {
+            for active_overlay in self.active_overlays.iter().rev() {
+                if let Some(env_vars) = scope.get(active_overlay) {
+                    if let Some(v) = env_vars.iter().find(|(k, _)| k.eq_ignore_case(name)) {
+                        return Some(v.1);
+                    }
+                }
+            }
+        }
+
+        for active_overlay in self.active_overlays.iter().rev() {
+            let is_hidden = if let Some(env_hidden) = self.env_hidden.get(active_overlay) {
+                env_hidden.iter().any(|k| k.eq_ignore_case(name))
+            } else {
+                false
+            };
+
+            if !is_hidden {
+                if let Some(env_vars) = engine_state.env_vars.get(active_overlay) {
+                    if let Some(v) = env_vars.iter().find(|(k, _)| k.eq_ignore_case(name)) {
+                        return Some(v.1);
+                    }
+                }
+            }
+        }
+        None
+    }
+
     pub fn has_env_var(&self, engine_state: &EngineState, name: &str) -> bool {
         for scope in self.env_vars.iter().rev() {
             for active_overlay in self.active_overlays.iter().rev() {