revert: perf: remove src directory from npm module (#6072)
revert: perf: remove src directory from npm module (#6072)

adding src dir back to npm package because projects that create
custom renderers (e.g. nativescript-vue) relie on it.

vuejs/vue,vuejs/vue,Hanks10100/vue,KingMario/vue,Kingwl/vue,vuejs/vue,KingMario/vue,Jinjiang/vue,Hanks10100/vue,Ddder-FE/vue,cnchanning/vue,vuejs/vue,Ddder-FE/vue,Ddder-FE/vue,Hanks10100/vue,cnchanning/vue,Jinjiang/vue,Ddder-FE/vue,KingMario/vue,KingMario/vue,Kingwl/vue,lizhiyao/vue,lizhiyao/vue,Jinjiang/vue,cnchanning/vue,Hanks10100/vue,Kingwl/vue,Kingwl/vue,Jinjiang/vue,lizhiyao/vue,optimizely/vue,lizhiyao/vue