repl: Customizable subprompt for multiline input

[pckrishnadas88]

Description:
This PR adds the ability to customise the REPL subprompt for multiline input. Previously, the REPL always used the fixed | prompt for multiline statements. With this change, the subprompt can be customised. Once feature finalised doc can be updated.

Feature: Customisable subprompt for multiline input.
Fixes : #59401

// custom-repl-subprompt.js
'use strict';
const repl = require('repl').start({ prompt: '> ' });

// Default behavior
// > const foo = {
// | bar: 42,
// | baz: 100
// | }
// > foo
// { bar: 42, baz: 100 }

// Set a custom multiline prompt
repl.setMultilinePrompt('... ');

// Example with custom prompt
// > const obj = {
// ... x: 1,
// ... y: 2
// ... }
// > obj
// { x: 1, y: 2 }

// Set an emoji as multiline prompt (UTF-8)
repl.setMultilinePrompt('😎 ');

// Example with emoji prompt
// > const emojiObj = {
// 😎 mood: 'happy',
// 😎 energy: 'high'
// 😎 }
// > emojiObj
// { mood: 'happy', energy: 'high' }

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.86%. Comparing base (b87312b) to head (3bbdf10).
⚠️ Report is 82 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/readline/interface.js	85.18%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #59566      +/-   ##
==========================================
- Coverage   89.87%   89.86%   -0.02%     
==========================================
  Files         656      667      +11     
  Lines      192947   195245    +2298     
  Branches    37840    38336     +496     
==========================================
+ Hits       173418   175463    +2045     
- Misses      12087    12224     +137     
- Partials     7442     7558     +116     

Files with missing lines	Coverage Δ
lib/internal/repl.js	100.00% <100.00%> (ø)
lib/repl.js	94.25% <100.00%> (+<0.01%)	⬆️
lib/internal/readline/interface.js	96.98% <85.18%> (-0.16%)	⬇️

... and 101 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.