(firefox) Add native ARM64 (win64-aarch64) support

[dennisameling]

Description

Detect the native OS architecture at install time and pick the matching Mozilla build via an architecture -> build map (x86/x64/arm64), so Windows on ARM installs the native win64-aarch64 build instead of the emulated x64 one.

• tools/chocolateyInstall.ps1: declare a per-package $builds map of architecture -> @{ Url; Checksum } and resolve the build via a shared Get-MozillaBuild helper. Resolution honors --forcex86 first, then the native arch from Chocolatey's Get-OSArchitecture (correct even under x64 emulation), falling back to x64 on older Chocolatey or when no arm64 checksum exists.
• tools/helpers.ps1 (shared with Thunderbird): GetChecksums also returns the win64-aarch64 checksum (patterns anchored so 64 and 64-aarch64 rows can't cross-match); add the shared Get-MozillaBuild architecture resolver.
• update_helper.ps1 (shared with Thunderbird): capture win64-aarch64 checksums from Mozilla SHA512SUMS, version each URL by its os= token, and add a shared GetMozillaUrlFormats emitting the x86/x64/arm64 URL formats.
• update.ps1: pass Win64Arm64Format through both streams.
• tools/LanguageChecksums.csv: add the win64-aarch64 checksum rows.

Verified installing the native arm64 build on Windows on ARM.

Motivation and Context

Companion PR to chocolatey/choco#3907 which aims to add native Windows arm64 support to Chocolatey.

How Has this Been Tested?

With a local build of a native arm64 choco.exe, I ran this command which resulted in a successful Firefox arm64 installation:

> choco install firefox -s "C:\repos\chocolatey-packages\automatic\firefox" -f -y --allow-unofficial
Chocolatey v2.8.0-windowsarm-20260607-e3472f8a

Chocolatey is not an official build (bypassed with --allow-unofficial).
 If you are seeing this message and it is not expected, your system may
 now be in a bad state. Only official builds are to be trusted.

Installing the following packages:
firefox
By installing, you accept licenses for the packages.
Firefox v151.0.3 already installed. Forcing reinstall of version '151.0.3'.
 Please use upgrade if you meant to upgrade to a new version.
Downloading package from source 'C:\repos\chocolatey-packages\automatic\firefox'

Firefox v151.0.3 (forced)
Firefox package files install completed. Performing other installation steps.
Using locale 'en-US'...
Downloading Firefox
  from 'https://download.mozilla.org/?product=firefox-151.0.3-ssl&os=win64-aarch64&lang=en-US'
Progress: 100% - Completed download of C:\Users\dennisameling\AppData\Local\Temp\chocolatey\Firefox\151.0.3\Firefox Setup 151.0.3.exe (77.44 MB).
Download of Firefox Setup 151.0.3.exe (77.44 MB) completed.
Hashes match.
Installing Firefox...
Firefox has been installed.
WARNING: No registry key found based on  'Mozilla Firefox'
 The install of Firefox was successful.
  Deployed to 'C:\Program Files\Mozilla Firefox'

Chocolatey installed 1/1 packages.
 See the log for details (C:\repos\choco\src\chocolatey.console\bin\Release\net48\logs\chocolatey.log).

Screenshot (if appropriate, usually isn't needed):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Migrated package (a package has been migrated from another repository)

Checklist:

• My pull request is not coming from the master branch.
• My code follows the code style of this repository.
• My change requires a change to documentation (this usually means the notes in the description of a package).
• I have updated the documentation accordingly (this usually means the notes in the description of a package).
• I have updated the package description and it is less than 4000 characters.
• All files are up to date with the latest Contributing Guidelines
• The added/modified package passed install/uninstall in the Chocolatey Test Environment. Note that we don't support the use of any other environment.
• The changes only affect a single package (not including meta package).