As far as I could evaluate, the typescript files are transpiled to JavaScript ES5 . So the issue is not that the IE doesn't know "import", because actually the the file you are importing is packed inside your "bundle.js" located in your "out" folder.
But, it seems to me that the files imported like import "yourfile" are not transpiled
import {getProposals} from "./data/Requests"; //this will be transpiled
import "./Core/Dummy.js"; //this is not transpiledSo in case Bing Maps doesn't have an npm package, maybe you can transpile the file yourself to ES5 before including it in the project, in order to have it working in IE.