Change parser to allow parsing two script tags on <script setup>

[ota-meshi]

This PR modifies the parser so that it can parse SFCs with two script tags.
However, the parser parses the two scripts only if the SFC has both <script setup> and plain <script>.

<script>
  performGlobalSideEffect()
  export const named = 1
</script>

<script setup>
  let count = 0
</script>

Related to #78

[ota-meshi]

Hmm. Can't parse the following SFCs well.

<script>
export let count = 42
</script>

<script setup>
let count = 42
</script>

The current PR implementation is a parse error because it parses as a single script.

export let count = 42

let count = 42

We need to parse it as a separate script, but I don't know how to merge the ScopeManager and parserServices generated by @typescript-eslint/parser.

[ota-meshi]

I also considered adding {} to the <script setup> script to make it look like block scope, but we can't do this because of the import statement.

<script>
export let count = 42
</script>

<script setup>
let count = 42
</script>

↓

export let count = 42

{
let count = 42
}

But the next SFC is an error.

<script>
export let count = 42
</script>

<script setup>
import Comp from './comp.vue'
let count = 42
</script>

↓

export let count = 42

{
import Comp from './comp.vue'
let count = 42
}

[ota-meshi]

Changed to parse <script setup> and split it into import statements and other statements to build source code.

For example:

<script>
export let count = 42
</script>

<script setup>
import MyComponent from './MyComponent.vue'
let count = 42
</script>

↓

export let count = 42
;
import MyComponent from './MyComponent.vue';
{
let count = 42
}