[webpack] fix translation calls in handlebars files

Fixes: CNVS-34067

Test plan:
* with webpack turned on and in prod mode
* run RAILS_ENV=production bundle exec rake canvas:compile_assets
* pick a different language on your user settings page (e.g.maori)
* go to /calendar
* the “week, Month, Agenda” buttons and everything
  else on the page should be translated into your language
* go to other pages, e.g. /courses/x/assignments/new
* all of the strings on those pages should be translated too

(The broken behavior was that any strings that came from handlebars
Files would not be translated but ones coming from js, erb or 
Coffeescript were)

Change-Id: I9a4b76e857b6c809b663d18abd7196ca10ef8564
Reviewed-on: https://gerrit.instructure.com/102534
Tested-by: Jenkins
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Simon Williams <simon@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>

Author: ryankshaw

frontend_build/i18nLinerHandlebars.js

@@ -12,6 +12,12 @@ const {allFingerprintsFor} = require('brandable_css/lib/main')
 const PreProcessor = require('./../gems/canvas_i18nliner/node_modules/i18nliner-handlebars/dist/lib/pre_processor')
 require('./../gems/canvas_i18nliner/js/scoped_hbs_pre_processor')
 
+// In this main file, we do a bunch of stuff to monkey-patch the default behavior of
+// i18nliner's HbsProcessor (specifically, we set the the `directories` and define a
+// `normalizePath` function so that translation keys stay relative to canvas root dir).
+// By requiring it here the code here will use that monkeypatched behavior.
+require('../gems/canvas_i18nliner/js/main')
+
 const compileHandlebars = (data) => {
   const path = data.path
   const source = data.source

gems/canvas_i18nliner/js/main.js

@@ -22,7 +22,7 @@ var ScopedTranslationHash = require("./scoped_translation_hash");
 
 // remove path stuff we don't want in the scope
 var pathRegex = new RegExp(
-  "^(" + HbsProcessor.prototype.directories.join("|") + ")(/plugins/[^/]+)?/"
+  ".*(" + HbsProcessor.prototype.directories.join("|") + ")(/plugins/[^/]+)?/"
 );
 ScopedHbsExtractor.prototype.normalizePath = function(path) {
   return path.replace(pathRegex, "").replace(/^([^\/]+\/)templates\//, '$1');