Convert most ts-ignore-calls to ts-expect-error (#93617)

Changes over to use ts-expect-error: https://devblogs.microsoft.com/typescript/announcing-typescript-3-9-beta/#ts-expect-error-comments

This revealed a number of places where we no longer need to supress errors

extensions/shared.webpack.config.js

@@ -68,7 +68,7 @@ module.exports = function withDefaults(/**@type WebpackConfig*/extConfig) {
 		// yes, really source maps
 		devtool: 'source-map',
 		plugins: [
-			// @ts-ignore
+			// @ts-expect-error
 			new CopyWebpackPlugin([
 				{ from: 'src', to: '.', ignore: ['**/test/**', '*.ts'] }
 			]),