[Rust] Tweak tmPreferences (sublimehq#3195)

* [Rust] Rename tmPreferences files

This commit renames all tmPreferences files to match the common naming
scheme used in all other packages.

* [Rust] Remove `name` field from tmPreferences files

* [Rust] Tweak Symbol List

This commit...

1. removes the following entries, which are defined in
   Default/Symbol List.tmPreferences:
   - `entity.name.enum`
   - `entity.name.function`
   - `entity.name.type`
2. adds:
   - `entity.name.constant.rust`
   - `entity.name.union`
3. adds a simple test for each symbol kind

Rust/RustComment.tmPreferences → Rust/Comments.tmPreferences

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <plist version="1.0">
 <dict>
-	<key>name</key>
-	<string>Rust Comments</string>
 	<key>scope</key>
 	<string>source.rust</string>
 	<key>settings</key>

Rust/RustIndent.tmPreferences → Rust/Indentation Rules.tmPreferences

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <plist version="1.0">
 <dict>
-	<key>name</key>
-	<string>Rust Indent</string>
 	<key>scope</key>
 	<string>source.rust</string>
 	<key>settings</key>

Rust/Symbol List.tmPreferences

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<plist version="1.0">
+<dict>
+	<key>scope</key>
+	<string>
+		entity.name.constant.rust,
+		entity.name.impl.rust,
+		entity.name.macro.rust,
+		entity.name.module.rust,
+		entity.name.struct.rust,
+		entity.name.trait.rust,
+		entity.name.union.rust
+	</string>
+	<key>settings</key>
+	<dict>
+		<key>showInSymbolList</key>
+		<integer>1</integer>
+		<key>showInIndexedSymbolList</key>
+		<integer>1</integer>
+	</dict>
+</dict>
+</plist>

Rust/tests/symbols/syntax_test_symbols.rs

@@ -0,0 +1,32 @@
+// SYNTAX TEST "Packages/Rust/Rust.sublime-syntax"
+
+fn foo() {}
+// @@@ definition
+
+enum MyEnum {}
+//   @@@@@@ definition
+
+macro_rules! my_macro []
+//           @@@@@@@@ definition
+
+mod my_mod { }
+//  @@@@@@ definition
+
+struct MyStruct {
+//     @@@@@@@@ definition
+
+    const A = 0;
+//        @ definition
+
+    fn bar() {}
+//     @@@ definition
+}
+
+trait MyTrait {}
+//    @@@@@@@ definition
+
+type MyType;
+//   @@@@@@ definition
+
+union Union {}
+//    @@@@@ definition