Add RunContext support for script outputs (#765)

Resolves #667

This PR:

- Introduces a new field in the project file: `scriptType` which has the
default value of `Class` (in parity with previous versions), but can
also be `RunContext`.
- This is then passed to `InstanceContext` from the `Project` struct.
- This then changes the RunContext in the lua `snapshot_middleware`

---------

Co-authored-by: Micah <dekkonot@rocketmail.com>

rojo-test/build-test-snapshots/end_to_end__tests__build__nested_runcontext.snap

@@ -0,0 +1,35 @@
+---
+source: tests/tests/build.rs
+expression: contents
+---
+<roblox version="4">
+  <Item class="Folder" referent="0">
+    <Properties>
+      <string name="Name">nested_runcontext</string>
+    </Properties>
+    <Item class="Folder" referent="1">
+      <Properties>
+        <string name="Name">folder1</string>
+      </Properties>
+      <Item class="Script" referent="2">
+        <Properties>
+          <string name="Name">test</string>
+          <token name="RunContext">1</token>
+          <string name="Source"></string>
+        </Properties>
+      </Item>
+    </Item>
+    <Item class="Folder" referent="3">
+      <Properties>
+        <string name="Name">folder2</string>
+      </Properties>
+      <Item class="Script" referent="4">
+        <Properties>
+          <string name="Name">test</string>
+          <token name="RunContext">0</token>
+          <string name="Source"></string>
+        </Properties>
+      </Item>
+    </Item>
+  </Item>
+</roblox>

rojo-test/build-test-snapshots/end_to_end__tests__build__script_meta_disabled.snap

@@ -11,6 +11,7 @@ expression: contents
       <Properties>
         <string name="Name">hello</string>
         <bool name="Disabled">true</bool>
+        <token name="RunContext">0</token>
         <string name="Source">-- This script should be marked 'Disabled'</string>
       </Properties>
     </Item>

rojo-test/build-test-snapshots/end_to_end__tests__build__server_in_folder.snap

@@ -10,6 +10,7 @@ expression: contents
     <Item class="Script" referent="1">
       <Properties>
         <string name="Name">serverScript</string>
+        <token name="RunContext">0</token>
         <string name="Source">-- This is a Lua server script</string>
       </Properties>
     </Item>

rojo-test/build-test-snapshots/end_to_end__tests__build__server_init.snap

@@ -6,6 +6,7 @@ expression: contents
   <Item class="Script" referent="0">
     <Properties>
       <string name="Name">server_init</string>
+      <token name="RunContext">0</token>
       <string name="Source">return "From folder/init.server.lua"</string>
     </Properties>
   </Item>

rojo-test/build-tests/nested_runcontext/default.project.json

@@ -0,0 +1,13 @@
+{
+  "name": "nested_runcontext",
+  "emitLegacyScripts": false,
+  "tree": {
+    "$className": "Folder",
+    "folder1": {
+      "$path": "folder1"
+    },
+    "folder2": {
+      "$path": "folder2"
+    }
+  }
+}

rojo-test/build-tests/nested_runcontext/folder2/default.project.json

@@ -0,0 +1,7 @@
+{
+  "name": "nested_runcontext",
+  "emitLegacyScripts": true,
+  "tree": {
+    "$path": "folder3"
+  }
+}

rojo-test/serve-test-snapshots/end_to_end__tests__serve__scripts_all-2.snap

@@ -24,6 +24,8 @@ instances:
     Name: bar
     Parent: id-2
     Properties:
+      RunContext:
+        Enum: 0
       Source:
         String: "-- Hello, from bar!"
   id-4:

rojo-test/serve-test-snapshots/end_to_end__tests__serve__scripts_all.snap

@@ -24,6 +24,8 @@ instances:
     Name: bar
     Parent: id-2
     Properties:
+      RunContext:
+        Enum: 0
       Source:
         String: "-- Hello, from bar!"
   id-4: