Use ESBuild for frontend build.

Replacing webpack by ESBuild for client code compilation (as in the
official quickstart plugin).

So we can remove deprecated webpack dependencies.

Note: webpack is still used for ConverseJS build.
This may be removed soon.

Related to issue #122.

build-client.js

@@ -0,0 +1,54 @@
+const path = require('path')
+const esbuild = require('esbuild')
+
+const packagejson = require('./package.json')
+const sourcemap = process.env.NODE_ENV === 'dev' ?  'inline' : false
+
+const clientFiles = [
+  // Client files list, without the file extension:
+  'common-client-plugin',
+  'videowatch-client-plugin',
+  'admin-plugin-client-plugin'
+]
+
+const configs = clientFiles.map(f => ({
+  entryPoints: [ path.resolve(__dirname, 'client', f + '.ts') ],
+  alias: {
+    'shared': path.resolve(__dirname, 'shared/')
+  },
+  define: {
+    PLUGIN_CHAT_PACKAGE_NAME: JSON.stringify(packagejson.name),
+    PLUGIN_CHAT_SHORT_NAME: JSON.stringify(packagejson.name.replace(/^peertube-plugin-/, ''))
+  },
+  bundle: true,
+  minify: true,
+  // FIXME: sourcemap:`true` does not work for now, because peertube does not serve static files.
+  // See https://github.com/Chocobozzz/PeerTube/issues/5185
+  sourcemap,
+  format: 'esm',
+  target: 'safari11',
+  outfile: path.resolve(__dirname, 'dist/client', f + '.js'),
+}))
+
+configs.push({
+  entryPoints: ["./conversejs/builtin.ts"],
+  bundle: true,
+  minify: true,
+  sourcemap,
+  target: 'safari11',
+  outfile: path.resolve(__dirname, 'dist/client/static', 'builtin.js'),
+})
+
+configs.push({
+  entryPoints: ["./client/settings.ts"],
+  bundle: true,
+  minify: true,
+  sourcemap,
+  target: 'safari11',
+  outfile: path.resolve(__dirname, 'dist/client/settings', 'settings.js'),
+})
+
+const promises = configs.map(c => esbuild.build(c))
+
+Promise.all(promises)
+  .catch(() => process.exit(1))