Remove webpack-userscript dependency

After weeks of debugging Better SweClockers' dark theme feature in
collaboration with users, we realized that the problem only occurred
with Tampermonkey, not with Violentmonkey.

SimonAlling/better-sweclockers#62

However, turns out it was our fault, not Tampermonkey's: We were
emitting metadata containing

    // @run_at document-start

instead of

    // @run-at document-start

because I forgot that we used to rely on the userscript-metadata package
to replace underscores with hyphens.

package.json

@@ -101,7 +101,6 @@
     "userscript-metadata": "^1.0.0",
     "webextension-manifest": "^1.0.0",
     "webpack": "^4.41.2",
-    "webpack-userscript": "^2.5.1",
     "yargs": "^15.0.2"
   }
 }

src/build/internal/webpack-plugin.ts

@@ -4,7 +4,13 @@ import Manifest from "webextension-manifest";
 import * as webpack from "webpack";
 import { RawSource } from "webpack-sources";
 
-import { BuildConfig, ENVIRONMENT_VARIABLES, EnvVarError, envVarName } from "./configuration";
+import {
+    BuildConfig,
+    ENVIRONMENT_VARIABLES,
+    EnvVarError,
+    distFileName,
+    envVarName,
+} from "./configuration";
 import * as Msg from "./messages";
 import { BuildConfigError } from "./validation";
 
@@ -17,7 +23,7 @@ export class UserscripterWebpackPlugin {
         envVarErrors: readonly EnvVarError[]
         envVars: ReadonlyArray<readonly [string, string | undefined]>
         manifest?: Manifest
-        metadataAssetName: string
+        metadataStringified: string
         metadataValidationResult: Metadata.ValidationResult<Metadata.Metadata>
         overriddenBuildConfig: BuildConfig
         verbose: boolean
@@ -28,22 +34,24 @@ export class UserscripterWebpackPlugin {
             buildConfigErrors,
             envVarErrors,
             envVars,
-            metadataAssetName,
+            metadataStringified,
             metadataValidationResult,
             manifest,
             overriddenBuildConfig,
             verbose,
         } = this.x;
-        if (manifest !== undefined) {
-            compiler.hooks.afterCompile.tap(
-                UserscripterWebpackPlugin.name,
-                compilation => {
+        const metadataAssetName = distFileName(overriddenBuildConfig.id, "meta");
+        compiler.hooks.afterCompile.tap(
+            UserscripterWebpackPlugin.name,
+            compilation => {
+                compilation.assets[metadataAssetName] = new RawSource(metadataStringified);
+                if (manifest !== undefined) {
                     compilation.assets[MANIFEST_FILE] = new RawSource(
                         JSON.stringify(manifest, null, MANIFEST_INDENTATION)
                     );
-                },
-            );
-        }
+                }
+            },
+        );
         compiler.hooks.afterEmit.tap(
             UserscripterWebpackPlugin.name,
             compilation => {

src/build/internal/webpack.ts

@@ -4,7 +4,6 @@ import TerserPlugin from "terser-webpack-plugin";
 import TsconfigPathsPlugin from "tsconfig-paths-webpack-plugin";
 import * as Metadata from "userscript-metadata";
 import * as webpack from "webpack";
-import WebpackUserscriptPlugin from "webpack-userscript";
 
 import {
     BuildConfig,
@@ -96,6 +95,7 @@ export function createWebpackConfig(x: WebpackConfigParameters): webpack.Configu
             version: finalVersion(unfinishedManifest.version),
         };
     })();
+    const finalMetadataStringified = Metadata.stringify(finalMetadata);
     // tslint:disable:object-literal-sort-keys
     return {
         mode: mode,
@@ -187,15 +187,15 @@ export function createWebpackConfig(x: WebpackConfigParameters): webpack.Configu
                 buildConfigErrors: buildConfigErrors(overridden.buildConfig),
                 envVarErrors: overridden.errors,
                 envVars: envVars(x.env),
+                metadataStringified: finalMetadataStringified,
                 metadataValidationResult: Metadata.validateWith(x.metadataSchema)(finalMetadata),
-                metadataAssetName: distFileName(overridden.buildConfig.id, "meta"),
                 manifest: finalManifest,
                 overriddenBuildConfig: overridden.buildConfig,
                 verbose: verbose,
             }),
-            new WebpackUserscriptPlugin({
-                metajs: true,
-                headers: finalMetadata,
+            new webpack.BannerPlugin({
+                banner: finalMetadataStringified,
+                raw: true,
             }),
         ],
         optimization: {