Localization refactoring:

* the front-end now use global constants, based on the translation key
* build-client.js use the ESBuild "define" directive to replace these
  globals at compile time, by the english value
* build:client must now be called after build:languages
* moving the loadLoc and loc backend functions in a separate lib

build-client.js

@@ -1,5 +1,6 @@
 const path = require('path')
 const esbuild = require('esbuild')
+const fs = require('fs')
 
 const packagejson = require('./package.json')
 const sourcemap = process.env.NODE_ENV === 'dev' ?  'inline' : false
@@ -11,15 +12,40 @@ const clientFiles = [
   'admin-plugin-client-plugin'
 ]
 
+function loadLocs() {
+  // Loading english strings, so we can inject them as constants.
+  const refFile = path.resolve(__dirname, 'dist', 'languages', 'en.reference.json')
+  if (!fs.existsSync(refFile)) {
+    throw new Error('Missing english reference file, please run "npm run build:languages" before building the client')
+  }
+  const english = require(refFile)
+
+  // Reading client/@types/global.d.ts, to have a list of needed localized strings.
+  const r = {}
+  const globalFile = path.resolve(__dirname, 'client', '@types', 'global.d.ts')
+  const globalFileContent = '' + fs.readFileSync(globalFile)
+  const matches = globalFileContent.matchAll(/^declare const LOC_(\w+)\b/gm)
+  for (const match of matches) {
+    const key = match[1].toLowerCase()
+    if (!(key in english) || (typeof english[key] !== 'string')) {
+      throw new Error('Missing english string key=' + key)
+    }
+    r['LOC_' + match[1]] = JSON.stringify(english[key])
+  }
+  return r
+}
+
+const define = Object.assign({
+  PLUGIN_CHAT_PACKAGE_NAME: JSON.stringify(packagejson.name),
+  PLUGIN_CHAT_SHORT_NAME: JSON.stringify(packagejson.name.replace(/^peertube-plugin-/, ''))
+}, loadLocs())
+
 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-/, ''))
-  },
+  define,
   bundle: true,
   minify: true,
   // FIXME: sourcemap:`true` does not work for now, because peertube does not serve static files.