Allow passing a custom compiler through options

[rigor789]

What problem does this feature solve?

I'm wondering if we could allow specifying a custom template compiler to be used here

vue-loader/lib/template-loader/index.js

Lines 88 to 91 in bd2581f

	const compile =
	isServer && compiler.ssrCompile && options.optimizeSSR !== false
	? compiler.ssrCompile
	: compiler.compile

The reason this would be useful is that we could more easily allow vue-loader to work with different platforms such as nativescript-vue.

Our goal is to keep feature parity with vue-loader, without having to maintain a fork which could easily get out of sync.

This would allow us to create a loader that is run before vue-loader, which would assemble a .vue file based on the targeted platform, and let vue-loader take care of the rest the same way it does for the web.

A more detailed write up of what we are working on can be found here: nativescript-vue#1

What does the proposed API look like?

I think it can be as simple as this

const compilerToUse = options.templateCompiler || compiler

const compile =
    isServer && compilerToUse.ssrCompile && options.optimizeSSR !== false
      ? compilerToUse.ssrCompile
      : compilerToUse.compile

[yyx990803]

This is supported in the next branch FYI. I can take a PR for master if you need it for v14 as well.

[rigor789]

Thank you! just tried with the next branch and this works really well! As for master, I don't think we need it right now, since our loader is still a work in progress, and I'll work with the next branch.