Rename all proposal plugins to -proposal- from -transform- (#6570)

packages/babel-plugin-proposal-function-sent/test/fixtures/function-sent/multiple/actual.js

@@ -0,0 +1,10 @@
+(function* () {
+  const a = function.sent;
+  const b = function.sent;
+  yield 4;
+  const c = function.sent;
+  const d = yield;
+  const e = function.sent;
+
+  return [ a, b, c, d, e ];
+}());