feat(compiler-sfc): new SFC css varaible injection implementation

ref: https://github.com/vuejs/rfcs/pull/231

packages/compiler-sfc/__tests__/utils.ts

@@ -0,0 +1,28 @@
+import { parse, SFCScriptCompileOptions, compileScript } from '../src'
+import { parse as babelParse } from '@babel/parser'
+import { babelParserDefaultPlugins } from '@vue/shared'
+
+export function compileSFCScript(
+  src: string,
+  options?: Partial<SFCScriptCompileOptions>
+) {
+  const { descriptor } = parse(src)
+  return compileScript(descriptor, {
+    ...options,
+    id: 'xxxxxxxx'
+  })
+}
+
+export function assertCode(code: string) {
+  // parse the generated code to make sure it is valid
+  try {
+    babelParse(code, {
+      sourceType: 'module',
+      plugins: [...babelParserDefaultPlugins, 'typescript']
+    })
+  } catch (e) {
+    console.log(code)
+    throw e
+  }
+  expect(code).toMatchSnapshot()
+}