feat: getBacklinksForFile change to return ReferenceCache

This is more a cosmetic change.
It's more accurate as reference can be either LinkCache or EmbedCache
However as types they are equivalent at the moment

src/obsidian/augmentations/MetadataCache.d.ts

@@ -66,7 +66,7 @@ declare module 'obsidian' {
         /**
          * Get all backlink information for a file
          */
-        getBacklinksForFile(file?: TFile): CustomArrayDict<LinkCache>;
+        getBacklinksForFile(file?: TFile): CustomArrayDict<ReferenceCache>;
         /**
          * Get paths of all files cached in the vault
          */