browser-support: Add string.prototype.startsWith polyfill.

Fixes #8944.
Adds string.prototype.startswith package to dependencies and places
it at `common` entry point in webpack.assets.json. As common.js is
loaded on all code paths first, there is no need to place this package
into other entry points.

package.json

@@ -32,6 +32,7 @@
     "script-loader": "0.7.2",
     "source-map-loader": "0.2.3",
     "string.prototype.codepointat": "0.2.0",
+    "string.prototype.startswith": "0.2.0",
     "to-markdown": "3.1.0",
     "ts-loader": "2.1.0",
     "ts-node": "3.3.0",

tools/webpack.assets.json

@@ -4,6 +4,7 @@
         "./static/js/portico/header.js"
     ],
     "common": [
+               "string.prototype.startswith",
                "./node_modules/jquery/dist/jquery.js",
                "./node_modules/underscore/underscore.js",
                "./static/js/blueslip.js",

version.py

@@ -8,4 +8,4 @@ ZULIP_VERSION = "1.7.1+git"
 # Typically, adding a dependency only requires a minor version bump, and
 # removing a dependency requires a major version bump.
 
-PROVISION_VERSION = '17.11'
+PROVISION_VERSION = '17.12'

yarn.lock

@@ -5980,6 +5980,10 @@ string.prototype.codepointat@0.2.0, string.prototype.codepointat@^0.2.0:
   version "0.2.0"
   resolved "https://registry.yarnpkg.com/string.prototype.codepointat/-/string.prototype.codepointat-0.2.0.tgz#6b26e9bd3afcaa7be3b4269b526de1b82000ac78"
 
+string.prototype.startswith@0.2.0:
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/string.prototype.startswith/-/string.prototype.startswith-0.2.0.tgz#da68982e353a4e9ac4a43b450a2045d1c445ae7b"
+
 string.prototype.trim@~1.1.2:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/string.prototype.trim/-/string.prototype.trim-1.1.2.tgz#d04de2c89e137f4d7d206f086b5ed2fae6be8cea"