Use consistent product name for 'Firefox Translations' in Fluent (Fixes #15442)

[Ayushsunny]

One-line summary

Treat "Firefox Translations" as a single product name in Fluent strings.

Significant changes and points to review

• Updated instances of { -brand-name-firefox } Translations to { -brand-name-firefox-translations } in relevant files.
• Ensured consistency by using the pre-defined { -brand-name-firefox-translations } entry from brands.ftl across all strings.
• Verified that the changes align with the Fluent localization standards for product naming.

Issue / Bugzilla link

Resolves Issue #15442

Testing

• Manually checked that each modified string renders "Firefox Translations" as a single entity in the UI.
• Confirmed the updated strings in different localization scenarios to ensure they display correctly.

[Ayushsunny]

Hiii @peiying2 , could you please review this PR? It addresses the issue you raised. Thank you!

[janbrasna]

I'm afraid this can't be changed without versioning the string — obsoleting the old, adding it as a fallback (thus changing the IDs in the actual template, too) — to make sure it updates in Pontoon properly, see: https://bedrock.readthedocs.io/en/latest/l10n.html#ftl-string-ids (and also the following § Obsolete strings and § Fallback chapters on that page…)

@peiying2 should confirm whether that's the case, but it usually is:/