feat: make this the implicit receiver for method calls inside class bodies

In the compiler, when a bare name is encountered inside a class definition and it does not resolve to a local variable or global, emit an implicit `this.` load before the call, enabling getter, setter, and method calls without explicit receiver. Update all benchmark, builtin, and test files to remove redundant `this.` qualifiers, and add comprehensive test suites for implicit receiver behavior across instance, inherited, static, nested, and shadowing scenarios.

test/implicit_receiver/inherited_methods.wren

@@ -0,0 +1,23 @@
+class Foo {
+  getter {
+    IO.print("getter")
+  }
+
+  setter = value {
+    IO.print("setter")
+  }
+
+  method(a) {
+    IO.print("method")
+  }
+}
+
+class Bar is Foo {
+  test {
+    getter            // expect: getter
+    setter = "value"  // expect: setter
+    method("arg")     // expect: method
+  }
+}
+
+(new Bar).test

test/implicit_receiver/instance_methods.wren

@@ -0,0 +1,23 @@
+class Foo {
+  getter {
+    IO.print("getter")
+  }
+
+  setter = value {
+    IO.print("setter")
+  }
+
+  method(a) {
+    IO.print("method")
+  }
+
+  test {
+    getter            // expect: getter
+    setter = "value"  // expect: setter
+    method("arg")     // expect: method
+  }
+}
+
+(new Foo).test
+
+// TODO: Need to decide how these interact with globals.

test/implicit_receiver/locals_shadow_getter.wren

@@ -0,0 +1,17 @@
+class Foo {
+  bar { return "getter" }
+
+  test {
+    IO.print(bar) // expect: getter
+
+    {
+      IO.print(bar) // expect: getter
+      var bar = "local"
+      IO.print(bar) // expect: local
+    }
+
+    IO.print(bar) // expect: getter
+  }
+}
+
+(new Foo).test

test/implicit_receiver/locals_shadow_setter.wren

@@ -0,0 +1,20 @@
+class Foo {
+  bar = value {
+    IO.print("setter")
+    return value
+  }
+
+  test {
+    bar = "value" // expect: setter
+
+    {
+      bar = "value" // expect: setter
+      var bar = "local"
+      bar = "value" // no expectation
+    }
+
+    bar = "value" // expect: setter
+  }
+}
+
+(new Foo).test

test/implicit_receiver/nested_class.wren

@@ -0,0 +1,47 @@
+class Outer {
+  getter {
+    IO.print("outer getter")
+  }
+
+  setter = value {
+    IO.print("outer setter")
+  }
+
+  method(a) {
+    IO.print("outer method")
+  }
+
+  test {
+    getter            // expect: outer getter
+    setter = "value"  // expect: outer setter
+    method("arg")     // expect: outer method
+
+    class Inner {
+      getter {
+        IO.print("inner getter")
+      }
+
+      setter = value {
+        IO.print("inner setter")
+      }
+
+      method(a) {
+        IO.print("inner method")
+      }
+
+      test {
+        getter            // expect: inner getter
+        setter = "value"  // expect: inner setter
+        method("arg")     // expect: inner method
+      }
+    }
+
+    (new Inner).test
+
+    getter            // expect: outer getter
+    setter = "value"  // expect: outer setter
+    method("arg")     // expect: outer method
+  }
+}
+
+(new Outer).test

test/implicit_receiver/static_methods.wren

@@ -0,0 +1,21 @@
+class Foo {
+  static getter {
+    IO.print("getter")
+  }
+
+  static setter = value {
+    IO.print("setter")
+  }
+
+  static method(a) {
+    IO.print("method")
+  }
+
+  static test {
+    getter            // expect: getter
+    setter = "value"  // expect: setter
+    method("arg")     // expect: method
+  }
+}
+
+Foo.test