Fix an error occurs in setDefaultLanguage.ps1 during the creation of an AVD custom image template

[Phoebe-0319]

Summary

Added a polling wait before Disable-ScheduledTask in SetDefaultLang.ps1, only on Build 22631 (Win11 23H2), only when the language was already installed by InstallLanguagePacks.ps1. This allows the ReconcileLanguageResources task (triggered by the WU+Restart between InstallLanguagePacks and SetDefaultLang) to finish delivering LpCab before the script disables it.

Flow comparison

                    BEFORE FIX (race condition)

InstallLanguagePacks.ps1          SetDefaultLang.ps1
========================          ==================

Disable tasks                     Disable tasks    <-- kills reconcile!
Install-Language ja-JP            "already installed" (skip)
  -> LanguagePacks: None          Set-systempreferreduilanguage
Enable tasks                        -> FAILS! (LpCab not ready)
                                  Enable tasks
        |
   WU + Restart
   (reconcile starts here,
    may or may not finish
    before SetDefaultLang)

                    AFTER FIX (deterministic)

InstallLanguagePacks.ps1          SetDefaultLang.ps1
========================          ==================

Disable tasks                     [23H2 only] Poll Get-InstalledLanguage
Install-Language ja-JP              until LanguagePacks != None
  -> LanguagePacks: None            (max 600s, 15s interval)
Enable tasks                      Disable tasks    <-- safe, reconcile done
                                  "already installed" (skip)
        |                         Set-systempreferreduilanguage
   WU + Restart                     -> SUCCESS (LpCab ready)
   (reconcile runs here)          Enable tasks

Timeline:

InstallLanguagePacks.ps1                    SetDefaultLang.ps1
    |                                           |
    |  Disable tasks                            |
    |  Install-Language (LanguagePacks=None)     |
    |  Enable tasks                             |
    |                                           |
    +------ WU + Restart ---------------------->|
    |       ^                                   |
    |       | reconcile task starts here        |
    |       | (triggered by restart)            |
    |       |                                   |
    |       | downloading LpCab...              | [NEW] Check: is LanguagePacks
    |       | downloading LpCab...              |        still "None"?
    |       | LpCab ready!                      |        YES -> wait 15s, retry
    |       v                                   |        ...
    |                                           |        YES -> wait 15s, retry
    |                                           |        NO  -> LpCab ready!
    |                                           |
    |                                           | Disable tasks (safe now)
    |                                           | "already installed" branch
    |                                           | Set-systempreferreduilanguage -> OK
    |                                           | Copy-UserInternationalSettings -> OK
    |                                           | Enable tasks
    |                                           |

Scope of change

• Only affects Win11 23H2 (Build 22631) -- all other OS versions skip the new code entirely
• Only polls when language was already installed by InstallLanguagePacks.ps1 -- if language is not installed, skips the wait
• Read-only polling -- uses Get-InstalledLanguage (no side effects)
• Max wait 600s (10 min) -- if reconcile doesn't finish, proceeds anyway with a WARNING log
• Zero impact on successful builds -- if reconcile already finished during WU+Restart, first poll returns ready, 0s added