refactor: rename jest presets (#4609)

* refactor: rename jest presets

Follow up of #4597.
Renamed `preset` folder to `presets`.
Added a default preset and it is accessible in the short form of
`@vue/cli-plugin-unit-jest`.

This change is inspired by ts-jest presets:
https://kulshekhar.github.io/ts-jest/user/config/#jest-preset

* fix: update import path

* fix: fix typo in file path

Author: haoqunjiang

packages/@vue/cli-plugin-unit-jest/generator/index.js

@@ -12,8 +12,8 @@ module.exports = (api, _, __, invoking) => {
     },
     jest: {
       preset: api.hasPlugin('babel')
-        ? '@vue/cli-plugin-unit-jest/preset'
-        : '@vue/cli-plugin-unit-jest/preset/no-babel'
+        ? '@vue/cli-plugin-unit-jest'
+        : '@vue/cli-plugin-unit-jest/presets/no-babel'
     }
   })
 
@@ -44,8 +44,8 @@ const applyTS = (module.exports.applyTS = (api, invoking) => {
   api.extendPackage({
     jest: {
       preset: api.hasPlugin('babel')
-        ? '@vue/cli-plugin-unit-jest/preset/typescript-and-babel'
-        : '@vue/cli-plugin-unit-jest/preset/typescript'
+        ? '@vue/cli-plugin-unit-jest/presets/typescript-and-babel'
+        : '@vue/cli-plugin-unit-jest/presets/typescript'
     },
     devDependencies: {
       '@types/jest': '^24.0.11'

packages/@vue/cli-plugin-unit-jest/jest-preset.js

@@ -0,0 +1 @@
+module.exports = require('./presets/default/jest-preset')

packages/@vue/cli-plugin-unit-jest/preset/jest-preset.js renamed to packages/@vue/cli-plugin-unit-jest/presets/default/jest-preset.js

@@ -1,5 +1,5 @@
 const deepmerge = require('deepmerge')
-const defaultPreset = require('../jest-preset')
+const defaultPreset = require('../default/jest-preset')
 
 // If no default babel preset exists,
 // we need to use a customized babel transformer to deal with es modules

packages/@vue/cli-plugin-unit-jest/preset/no-babel/esmoduleTransformer.js renamed to packages/@vue/cli-plugin-unit-jest/presets/no-babel/esmoduleTransformer.js

@@ -1,5 +1,5 @@
 const deepmerge = require('deepmerge')
-const defaultPreset = require('../jest-preset')
+const defaultPreset = require('../default/jest-preset')
 
 module.exports = deepmerge(
   defaultPreset,