XDG_BASE_DIR support (linux, windows) (#10808)

This PR adds XDG_BASE_DIR support on linux, and cleans up the path
declarations slightly. Additionally, we move the embeddings and
conversations directly to the SUPPORT_DIR on those platforms.
I _think_ that should also be done on MacOS in the future, but that has
been left out here for now to not break existing users setups.

Additionally, we move the SUPPORT_DIR into LocalAppData on windows for
consistency.

Release Notes:

- Fixed missing support of `XDG_BASE_DIR` on linux
- Fixed improper placement of data in XDG_CONFIG_HOME on linux and
windows (https://github.com/zed-industries/zed/issues/9308,
https://github.com/zed-industries/zed/issues/7155)

---------

Co-authored-by: phisch <philipp.schaffrath@gmail.com>

crates/zed/src/main.rs

@@ -925,7 +925,11 @@ async fn upload_previous_crashes(
 
     let crash_report_url = http.build_zed_api_url("/telemetry/crashes", &[])?;
 
-    for dir in [&*CRASHES_DIR, &*CRASHES_RETIRED_DIR] {
+    // crash directories are only set on MacOS
+    for dir in [&*CRASHES_DIR, &*CRASHES_RETIRED_DIR]
+        .iter()
+        .filter_map(|d| d.as_deref())
+    {
         let mut children = smol::fs::read_dir(&dir).await?;
         while let Some(child) = children.next().await {
             let child = child?;