Remove InstanceSnapshotContext in favor of InstanceContext (#271)

* Drop plugin context on the floor

* Remove redirect from old context to new context

* Pass InstanceContext via & instead of &mut reference

* Re-use context value in ChangeProcessor from metadata

src/snapshot_middleware/middleware.rs

@@ -1,18 +1,18 @@
 use rbx_dom_weak::{RbxId, RbxTree};
 
 use crate::{
-    snapshot::InstanceSnapshot,
+    snapshot::{InstanceContext, InstanceSnapshot},
     vfs::{Vfs, VfsEntry, VfsFetcher, VfsSnapshot},
 };
 
-use super::{context::InstanceSnapshotContext, error::SnapshotError};
+use super::error::SnapshotError;
 
 pub type SnapshotInstanceResult = Result<Option<InstanceSnapshot>, SnapshotError>;
 pub type SnapshotFileResult = Option<(String, VfsSnapshot)>;
 
 pub trait SnapshotMiddleware {
     fn from_vfs<F: VfsFetcher>(
-        context: &mut InstanceSnapshotContext,
+        context: &InstanceContext,
         vfs: &Vfs<F>,
         entry: &VfsEntry,
     ) -> SnapshotInstanceResult;