vuejs / composition-api

* feat(getCurrentInstance): Aligning with vue3
BREAKING CHANGE: The internal vm can be accessed with `getCurrentInstance().proxy`

```js
const vm = getCurrentInstance()

// becomes

const vm = getCurrentInstance().proxy
```

* chore: improve

* changes

* update tests

* chore: add tests

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>

* Update README.md

* Fix type of SetupContext.ref

* Remove redundant docs

* Update readme

* Move "Browser Compatibility" section

* feat: add type-level `readonly()` api

* Update src/reactivity/readonly.ts

* chore: update tests

…onent (#610)

* feat: add warn

* test: add test for warn

* chore(README): point to v3 composition api docs

* update cn README too

)

Co-authored-by: lantian.tlan <lantian.tlan@bytedance.com>

* Update CHANGELOG.md

closes [this issue](#577)

* Update CHANGELOG.md

…es (#567)

Co-authored-by: vail <ysywix@gmail.com>

Co-authored-by: Javier Pérez <kiroushi@gmail.com>

Co-authored-by: Carlos Rodrigues <david-181@hotmail.com>

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>

BREAKING CHANGE: watch APIs now default to use `flush: 'pre'` instead of
`flush: 'post'`.

  - Check vuejs/vue-next@49bb447 

  - This change affects `watch`, `watchEffect`, the `watch` component
    option, and `this.$watch`.

  - As pointed out by @skirtles-code in
    [this comment](#1706 (comment)),
    Vue 2's watch behavior is pre-flush, and the ecosystem has many uses
    of watch that assumes the pre-flush behavior. Defaulting to post-flush
    can result in unnecessary re-renders without the users being aware of
    it.

  - With this change, watchers need to specify `{ flush: 'post' }` via
    options to trigger callback after Vue render updates. Note that
    specifying `{ flush: 'post' }` will also defer `watchEffect`'s
    initial run to wait for the component's initial render.

…532)

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>