fix(compiler-core): add isTemplateFor to ast of For nodes

[Tofandel]

There is an inconsistency in the generated ast between v-for and v-if, the v-for only returns a For node with it's direct children, the v-if returns one decorative wrapper node containing the branch nodes as children

Here is a demonstration https://codesandbox.io/p/sandbox/priceless-cache-t7zwzg

While we can work around this inconsistency for the most part, the original node properties on the v-for are entirely lost, there is just no way to know if the node is a template or an element by looking at it to reverse engineer the ast

Even the loc.source does not give this information like the v-if does (unless looking into the codeGen.loc.source)

The IfNode also has a boolean property isTemplateIf which also gives this information

Here is the difference in loc between a v-for

{
    start: { column: 3, line: 3, offset: 13 },
    end: { column: 24, line: 3, offset: 34 },
    source: 'v-for="test in test2"'
  }

and a v-if

{
    start: { column: 1, line: 2, offset: 1 },
    end: { column: 12, line: 5, offset: 55 },
    source: '<template\n    v-if="test">\n    <div></div>\n</template>'
}

As we can see the v-for completely drops it's parent information and uses the information of the Directive, while the v-if uses the information of the Element on which it was found

This PR aims to aleviate a bit this loss of information by adding a isTemplateFor and a templateProps property to the ForNode to indicate whether the original is a template or an element to know how to interpret the children nodes properly and to be able to retrieve the key directive on the template when we reverse engineer the AST

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	85.8 kB	32.6 kB	29.4 kB
vue.global.prod.js	132 kB (+51 B)	49.3 kB (+17 B)	44.3 kB (-52 B)

Usages

Name	Size	Gzip	Brotli
createApp	47.7 kB	18.9 kB	17.2 kB
createSSRApp	50.5 kB	19.9 kB	18.2 kB
defineCustomElement	50.1 kB	19.6 kB	17.9 kB
overall	61.1 kB	23.7 kB	21.6 kB

[skirtles-code]

I was hoping to review this, but I'm unclear what the use case is. Is there a specific tool/library that would benefit from including this extra information?

[Tofandel]

It's not really extra information, it's information that is missing that is normally available. I was trying to build a tool that would have used it, and this is crucial information that is missing, without it there is no way to know what node/tag is the v for on

Without it we cannot edit the existing source as the original source of the ast is incomplete without it