Add Luau-style ref paths migration plan and update related tests

- Introduced a new migration plan for converting `Rojo_Ref_*` attribute paths to Luau require-by-string style, enhancing portability with relative paths.
- Updated existing test snapshots to reflect the new path formats, ensuring consistency across various scenarios.
- Enhanced the `compute_relative_ref_path` and `resolve_ref_path` functions to support the new path semantics, improving path resolution logic.
- Refactored related code in `change_processor`, `syncback`, and `snapshot` modules to accommodate the new reference path handling.

These changes improve the robustness and maintainability of reference path management in the project.

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__duplicate_rojo_id-container.model.json5.snap

@@ -7,7 +7,7 @@ expression: container.model.json5
     {
       attributes: {
         Rojo_Id: "value_1",
-        Rojo_Ref_Value: "ReplicatedStorage/container/value_1.model.json5"
+        Rojo_Ref_Value: "@self"
       },
       className: "ObjectValue",
       name: "value_1"
@@ -15,7 +15,7 @@ expression: container.model.json5
     {
       attributes: {
         Rojo_Id: "value_1",
-        Rojo_Ref_Value: "ReplicatedStorage/container/value_2.model.json5"
+        Rojo_Ref_Value: "@self"
       },
       className: "ObjectValue",
       name: "value_2"

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties-src__pointer.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/pointer.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "target.model.json5"
+    Rojo_Ref_Value: "@game/target.model.json5"
   },
   className: "ObjectValue"
 }

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_blank-src__pointer.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/pointer.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "target.txt"
+    Rojo_Ref_Value: "@game/target.txt"
   },
   className: "ObjectValue"
 }

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_conflict-src__Pointer_2.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/Pointer_2.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "Target_2.model.json5"
+    Rojo_Ref_Value: "@game/Target_2.model.json5"
   },
   className: "ObjectValue"
 }

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer1.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/Pointer1.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "ReplicatedStorage/Target1.model.json5"
+    Rojo_Ref_Value: "@game/ReplicatedStorage/Target1.model.json5"
   },
   className: "ObjectValue"
 }

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer2.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/Pointer2.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "ReplicatedStorage/Target2.model.json5"
+    Rojo_Ref_Value: "@game/ReplicatedStorage/Target2.model.json5"
   },
   className: "ObjectValue"
 }

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer3.model.json5.snap

@@ -4,7 +4,7 @@ expression: src/Pointer3.model.json5
 ---
 {
   attributes: {
-    Rojo_Ref_Value: "ReplicatedStorage/Target3.model.json5"
+    Rojo_Ref_Value: "@game/ReplicatedStorage/Target3.model.json5"
   },
   className: "ObjectValue"
 }