perf(core): use for-of instead of while for getFieldValue
perf(core): use for-of instead of while for getFieldValue

ngx-formly/ngx-formly,ngx-formly/ngx-formly,formly-js/ng-formly,ngx-formly/ngx-formly,ngx-formly/ngx-formly,formly-js/ng2-formly,formly-js/ng2-formly,formly-js/ng-formly,formly-js/ng2-formly