Restructure find_path into a separate functions for modules and non-module items

Also renames `prefer_core` imports config to `prefer_no_std` and changes the behavior of no_std path searching by preferring `core` paths `over` alloc

crates/ide-completion/src/config.rs

@@ -17,7 +17,7 @@ pub struct CompletionConfig {
     pub callable: Option<CallableSnippets>,
     pub snippet_cap: Option<SnippetCap>,
     pub insert_use: InsertUseConfig,
-    pub prefer_core: bool,
+    pub prefer_no_std: bool,
     pub snippets: Vec<Snippet>,
 }