spoof english leaks via numberingSystem: numbers (non-latn) or decimal separator (latn)

we only currently have three (locale, numberingSystem): ar (arab), fa (arabext) and my (mymr)

PREREQ

• see this: https://searchfox.org/mozilla-central/source/dom/locales/en-US/chrome/dom/dom.properties
• note some validations have $S to pass values (like dates and numbers)
• test: https://arkenfox.github.io/TZP/tests/applang.html
  • it's also built into TZP (https://arkenfox.github.io/TZP/tzp.html#region) where you get health checks
  • note: both pages do not set a language in the html tag
• get an en-US default hash/strings [1]

[1] for reference, this is en-US

DOCUMENT: validation_messages: ca1379a9
{
  "BadInputNumber": "Please enter a number.",
  "CheckboxMissing": "Please check this box if you want to proceed.",
  "DateTimeRangeOverflow": "Please select a value that is no later than 2023-12-31.",
  "DateTimeRangeUnderflow": "Please select a value that is no earlier than 2023-12-31.",
  "FileMissing": "Please select a file.",
  "InvalidEmail": "Please enter an email address.",
  "InvalidURL": "Please enter a URL.",
  "NumberRangeOverflow": "Please select a value that is no more than 2.",
  "NumberRangeUnderflow": "Please select a value that is no less than 2.",
  "PatternMismatch": "Please match the requested format.",
  "RadioMissing": "Please select one of these options.",
  "SelectMissing": "Please select an item in the list.",
  "StepMismatch": "Please select a valid value. The two nearest valid values are 2 and 4.",
  "ValueMissing": "Please fill out this field."
}

STR

• change app language to ar, fa, or my and restart to apply
• change to spoof english
• test

ER

• you get the en-US hash

AR

• you don't get the expected en_US hash (pic is ar)
• 

ANALYSIS

• dates: this seems to always be 2023-12-31 format regardless of locale, this is the valid set in the element's min or max value. It can change order on RTL (when not spoofing as english) e.g. 31-12-2023 but that is because of RTL not formatting, so I think dates are not affected
• numbers - not all validation messages with numbers were affected, so this is definitely fixable
• the only line that failed to get spoofed (in my tests which may/maynot be exhaustive) is the one in the pic

here's the hashes when spoofing as en-US (yes, the arabext 4 is different from the arab 4) and en-US for comparison

      numberingSystem
app:      |       hash:  string:
 ar:    arab: a74be209: "Please select a valid value. The two nearest valid values are ٢ and ٤.",
 fa: arabext: a4227729: "Please select a valid value. The two nearest valid values are ۲ and ۴.",
 my:    mymr: 36e68dc9: "Please select a valid value. The two nearest valid values are ၂ and ၄."
 en:    latn: ca1379a9: "Please select a valid value. The two nearest valid values are 2 and 4."

cc @pierov @tjr