regression: timezone field blank for legacy aliases

[dougfabris]

Proposed changes (including videos or screenshots)

Summary

Restores compatibility for legacy timezone aliases (UTC, Etc/UTC, US/Pacific, Japan, …) that were lost when #40076 migrated the timezone list from moment.tz.names() (597 zones) to Intl.supportedValuesOf('timeZone') (418 zones). Any Select fed by useTimezoneNameList — Business Hours and the admin Timezone setting — rendered empty for workspaces whose saved value was one of the 179 dropped aliases.

• Add canonicalizeTimezone in @rocket.chat/tools — resolves legacy aliases to their canonical IANA zone via Intl.DateTimeFormat, falling back to the input on invalid values.
• Ensure UTC is always present in useTimezoneNameList, since Intl.supportedValuesOf omits it on several ICU versions.
• Apply canonicalization when loading the saved value in EditBusinessHours and SelectTimezoneSettingInput, so existing documents render correctly and are gradually rewritten to canonical form on save.

Test plan

• On a workspace with a Business Hour saved as timezone.name === "UTC" (pre-8.4), open it on this branch — field shows UTC, save persists UTC.
• Repeat with US/Pacific — field shows America/Los_Angeles, saves as America/Los_Angeles.
• Admin → General → Timezone: a legacy-aliased value loads into the select.

Issue(s)

Steps to test or reproduce

Further comments

CORE-2135

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[codecov]

Codecov Report

❌ Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.97%. Comparing base (92dbb53) to head (9b69d16).
⚠️ Report is 1 commits behind head on release-8.4.0.

Additional details and impacted files

@@                Coverage Diff                @@
##           release-8.4.0   #40305      +/-   ##
=================================================
+ Coverage          69.74%   69.97%   +0.22%     
=================================================
  Files               3298     3299       +1     
  Lines             119292   120106     +814     
  Branches           21469    21499      +30     
=================================================
+ Hits               83206    84043     +837     
+ Misses             32785    32776       -9     
+ Partials            3301     3287      -14     

Flag	Coverage Δ
e2e	59.65% <25.00%> (-0.02%)	⬇️
e2e-api	46.23% <ø> (-0.04%)	⬇️
unit	70.82% <10.00%> (+0.31%)	⬆️

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