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 119 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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.