Bitcoin.com NTP widget fiat updates [1.15]

[ryanml]

Uplift of #6790, #6783
Fixes: brave/brave-browser#12016, brave/brave-browser#11996

Approved, please ensure that before merging:

• You have checked CI and the builds, lint, and tests all pass or are not related to your PR.
• You have tested your change on Nightly.
• The PR milestones match the branch they are landing to.

After you merge:

• The associated issue milestone is set to the smallest version that the changes is landed on.

[kjozwiak]

Restarting macOS via https://ci.brave.com/job/pr-brave-browser-bdc-fiat-updates-1.15-macos/2/ using WIPE_WORKSPACE due to init failing as per https://ci.brave.com/job/pr-brave-browser-bdc-fiat-updates-1.15-macos/1/execution/node/104/log/.

15:29:02  Error: Command 'vpython src/third_party/depot_tools/download_from_google_storage.py --no_resume --directory --recursive --no_auth --num_threads=16 --bucket chromium-apache-mac src/third_party/apache-mac' returned non-zero exit status 1 in /Users/jenkins/jenkins/workspace/pr-brave-browser-bdc-fiat-updates-1.15-macos
15:29:02  Hook 'vpython src/third_party/depot_tools/download_from_google_storage.py --no_resume --directory --recursive --no_auth --num_threads=16 --bucket chromium-apache-mac src/third_party/apache-mac' took 24.35 secs

[kjozwiak]

Uplift into 1.15.x approved after deliberating with @brave/uplift-approvers. QA has verified the PR on Nightly as per #6790 (comment).

However, #6783 didn't end up fixing brave/brave-browser#11996 so we'll fix it in a follow up once 1.15.x HF1 is released. Will be addressed via brave/brave-browser#12028.