Move LWC to peer dependency

[nolanlawson]

Right now lwc-webpack-plugin relies on explicit versions of LWC:

lwc-webpack-plugin/package.json

Lines 36 to 41 in 7e9cbc5

	"@lwc/babel-plugin-component": "~2.5.2",
	"@lwc/compiler": "~2.5.2",
	"@lwc/engine-dom": "~2.5.2",
	"@lwc/module-resolver": "~2.5.2",
	"@lwc/synthetic-shadow": "~2.5.2",
	"@lwc/wire-service": "~2.5.2",

These should be moved to peerDependencies, because consumers of this plugin should be able to use whatever version of LWC they want, as long as it's compatible (2.x basically).

Note that this would be a breaking change.