Devtool uses eval-cheap-module-source-map by default

[keeplz]

What problem does this feature solve?

When i want to use sourcemap like 'eval-source-map' with chainWebapck, it doesn't work.

Because it will be changed by cli in silence, is this reasonable? or it is a bug.

vue-cli/packages/@vue/cli-service/lib/commands/serve.js

Lines 51 to 54 in 89af6c5

	api.chainWebpack(webpackConfig => {
	if (process.env.NODE_ENV !== 'production' && process.env.NODE_ENV !== 'test') {
	webpackConfig
	.devtool('eval-cheap-module-source-map')

For now, i use configureWebpack to get this.

What does the proposed API look like?

if user user set devtool in chainWebapck, cli shouldn't change it in silence, or even a waning will be better