Adds partially concat support

[tronsha]

This example works:

<template>
    <div :style="'fontSize: ' + (size + 10) + 'px'"></div> 
</template>

<script>
export default {
  props: {
    size: {
      type: number,
      required: true,
    },
  },
};
</script>

<div style="{{ 'fontSize: ' ~ (size + 10) ~ 'px' }};"></div>

But this example doesn't work correct:

<template>
    <div :style="'fontSize: ' + (foo.size + 10) + 'px'"></div> 
</template>

<script>
export default {
  props: {
    foo: {
      type: object,
      required: true,
    },
  },
};
</script>

<div style="{{ 'fontSize: ' ~ (foo.size ~ 10) ~ 'px' }};"></div>