chore: Remove /internal/i18n in favor of /i18n

[avinashbot]

Description

Okay, so... everyone we asked to use /internal/i18n before we released it has switched out to /i18n. Let's nip this tech debt in the bud.

Most of it is path updates. The only meaningful changes are under build-tools and src/internal/i18n (now gone).

Related links, issue #, if available: n/a

How has this been tested?

Existing tests should pass. Also manually inspected the built messages to make sure everything checked out.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (8d643d6) 93.46% compared to head (6db2cc4) 93.47%.
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1382   +/-   ##
=======================================
  Coverage   93.46%   93.47%           
=======================================
  Files         623      624    +1     
  Lines       16764    16778   +14     
  Branches     5547     5550    +3     
=======================================
+ Hits        15669    15683   +14     
  Misses       1022     1022           
  Partials       73       73           

Files Changed	Coverage Δ
src/alert/internal.tsx	100.00% <ø> (ø)
src/app-layout/index.tsx	93.49% <ø> (ø)
src/area-chart/elements/use-highlight-details.ts	100.00% <ø> (ø)
src/attribute-editor/row.tsx	96.66% <ø> (ø)
src/autosuggest/autosuggest-option.tsx	86.95% <ø> (ø)
src/autosuggest/internal.tsx	96.05% <ø> (ø)
src/breadcrumb-group/internal.tsx	86.84% <ø> (ø)
src/calendar/internal.tsx	98.07% <ø> (ø)
src/cards/index.tsx	93.90% <ø> (ø)
src/code-editor/index.tsx	96.50% <ø> (ø)
... and 53 more

... and 3 files with indirect coverage changes

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