tzset: Fix timezone extraction not working for all languages (#22250)

With certain language I've noticed that the timezone extraction
algorithm doesn't work.  or example consider the following:


Test file:
```JavaScript
const date = new Date();
console.log(date.toLocaleTimeString(undefined, {hour12: false, timeZoneName: 'short'}))
```

Run test file with specific local such as `th-TH` or `ar-AE`
```bash
LC_ALL="th-TH" TZ="Asia/Bangkok" node test.js
# prints "15 นาฬิกา 53 นาที 54 วินาที GMT+7"
```
And so the current logic for extracting would fail and return "นาฬิกา" (second item when splitting by space)

In this PR, a new approach is proposed for extracting the timezone offset and tests are updated with new test-case


See #21596

Author: efyx

src/library.js

@@ -657,9 +657,20 @@ addToLibrary({
 
     {{{ makeSetValue('daylight', '0', 'Number(winterOffset != summerOffset)', 'i32') }}};
 
-    var extractZone = (date) => date.toLocaleTimeString(undefined, {hour12:false, timeZoneName:'short'}).split(' ')[1];
-    var winterName = extractZone(winter);
-    var summerName = extractZone(summer);
+    var extractZone = (timezoneOffset) => {
+      // Why inverse sign?
+      // Read here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset
+      var sign = timezoneOffset >= 0 ? "-" : "+";
+
+      var absOffset = Math.abs(timezoneOffset)
+      var hours = String(Math.floor(absOffset / 60)).padStart(2, "0");
+      var minutes = String(absOffset % 60).padStart(2, "0");
+
+      return `UTC${sign}${hours}${minutes}`;
+    }
+
+    var winterName = extractZone(winterOffset);
+    var summerName = extractZone(summerOffset);
 #if ASSERTIONS
     assert(winterName);
     assert(summerName);

test/test_other.py

@@ -36,7 +36,7 @@
 from common import create_file, parameterized, NON_ZERO, node_pthreads, TEST_ROOT, test_file
 from common import compiler_for, EMBUILDER, requires_v8, requires_node, requires_wasm64, requires_node_canary
 from common import requires_wasm_exnref, crossplatform, with_all_eh_sjlj, with_all_sjlj
-from common import also_with_standalone_wasm, also_with_env_modify, also_with_wasm2js
+from common import also_with_standalone_wasm, also_with_wasm2js
 from common import also_with_minimal_runtime, also_with_wasm_bigint, also_with_wasm64, flaky
 from common import EMTEST_BUILD_VERBOSE, PYTHON, WEBIDL_BINDER
 from common import requires_network, parameterize
@@ -5942,11 +5942,20 @@ def test_force_stdlibs(self):
     self.do_runf('hello_world.c', emcc_args=['-sWASM_BIGINT'])
 
   @crossplatform
-  @also_with_env_modify({'gb_locale': {'LC_ALL': 'en_GB'}, 'long_tz': {'TZ': 'Asia/Kathmandu'}})
   def test_strftime_zZ(self):
-    if os.environ.get('LC_ALL') == 'en_GB' and MACOS:
+    if MACOS:
       self.skipTest('setting LC_ALL is not compatible with macOS python')
-    self.do_runf('other/test_strftime_zZ.c', 'ok!')
+
+    tz_lang_infos = [
+      {'env': {'LC_ALL': 'en_GB', 'TZ': 'Europe/London'}, 'expected_utc': 'UTC+0100'},
+      {'env': {'LC_ALL': 'th_TH', 'TZ': 'Asia/Bangkok'}, 'expected_utc': 'UTC+0700'},
+      {'env': {'LC_ALL': 'ar-AE', 'TZ': 'Asia/Dubai'}, 'expected_utc': 'UTC+0400'},
+      {'env': {'LC_ALL': 'en-US', 'TZ': 'America/Los_Angeles'}, 'expected_utc': 'UTC-0700'}
+    ]
+
+    for tz_lang_info in tz_lang_infos:
+      with env_modify(tz_lang_info['env']):
+        self.do_runf('other/test_strftime_zZ.c', 'The current timezone is: %s' % (tz_lang_info['expected_utc']))
 
   def test_strptime_symmetry(self):
     self.do_other_test('test_strptime_symmetry.c')