Use helix-stdx tilde expansion and normalization for HELIX_RUNTIME paths

Previously this wasn't possible since helix-core depends on helix-loader,
so helix-loader couldn't use helix-core's path extensions.

We use the path normalization/canonicalization for the runtime directory
provided by the HELIX_RUNTIME environment variable. This improves a
scenario where you set a path containing a tilde. Now that path will be
expanded and normalized.

Cargo.lock

@@ -1114,6 +1114,7 @@ dependencies = [
  "cc",
  "dunce",
  "etcetera",
+ "helix-stdx",
  "libloading",
  "log",
  "once_cell",

helix-loader/Cargo.toml

@@ -15,6 +15,8 @@ name = "hx-loader"
 path = "src/main.rs"
 
 [dependencies]
+helix-stdx = { path = "../helix-stdx" }
+
 anyhow = "1"
 serde = { version = "1.0", features = ["derive"] }
 toml = "0.7"

helix-loader/src/lib.rs

@@ -53,7 +53,8 @@ fn prioritize_runtime_dirs() -> Vec<PathBuf> {
     rt_dirs.push(conf_rt_dir);
 
     if let Ok(dir) = std::env::var("HELIX_RUNTIME") {
-        rt_dirs.push(dir.into());
+        let dir = path::expand_tilde(dir);
+        rt_dirs.push(path::normalize(dir));
     }
 
     // If this variable is set during build time, it will always be included