repl: add auto-indentation for multiline input

[hemanth]

Split from #64443 per review feedback to use idiomatic single-feature PRs.

Automatically inserts 2-space indentation on continuation lines based on the current nesting depth of braces, brackets, and parentheses.

Refs: #48164

[hemanth]

• setupAutoIndent → standalone getAutoIndent(code) helper, no more monkey-patching the REPL instance
• Dropped the typeof guard — direct call since the helper is always available
• Swapped manual char scanner for Acorn tokenizer (same one used in isRecoverableError), falls back to simple brace-counting on parse failure

PTAL @avivkeller

[hemanth]

Good call — dropped the Acorn re-parse entirely. isRecoverableError already validates syntax before getAutoIndent runs, so a simple brace counter is sufficient here. Lighter and no duplicate work 👍

PTAL @avivkeller

[codecov]

Codecov Report

❌ Patch coverage is 98.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.12%. Comparing base (0bcc6ef) to head (aa16617).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/repl/utils.js	98.07%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64607      +/-   ##
==========================================
- Coverage   90.14%   90.12%   -0.02%     
==========================================
  Files         741      741              
  Lines      242080   242140      +60     
  Branches    45563    45575      +12     
==========================================
+ Hits       218213   218239      +26     
- Misses      15375    15425      +50     
+ Partials     8492     8476      -16     

Files with missing lines	Coverage Δ
lib/repl.js	92.96% <100.00%> (+0.04%)	⬆️
lib/internal/repl/utils.js	96.99% <98.07%> (+0.06%)	⬆️

... and 36 files with indirect coverage changes

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