Fix RTL plugin crash with empty formatted text sections

[Omkarthipparthi]

Description

Fixes crash when using RTL text plugin with formatted text-field expressions where all sections evaluate to empty strings.

Closes #6444

Problem

When using the RTL text plugin (@mapbox/[email protected]) with a formatted text-field where all sections are empty (e.g., both name and ref are null), the application crashes with:

Root Cause

The RTL plugin's processStyledBidirectionalText can return either:

• Tuples: [text, sectionIndex] (expected format)
• Objects: {text, sectionIndex} (some plugin versions/edge cases)

The shaping code in src/symbol/shaping.ts only handled tuples, causing taggedLine.text to be undefined when objects were returned, leading to crashes when later code accessed this.text.length.

Solution

Added defensive normalization logic (lines 331-361 in shaping.ts) to:

• Accept both tuple [text, sectionIndex] and object {text, sectionIndex} formats
• Provide safe fallbacks: empty string '' for text, empty array [] for sectionIndex
• Maintain backward compatibility with all RTL plugin versions

Testing

• All 17 integration shaping tests pass
• All 2476 unit tests pass (including 10 shaping-specific tests)
• Tested locally with @mapbox/[email protected]
• No regressions in existing functionality

Test Cases Verified

1. Empty formatted sections (the bug repro) - No crash
2. Arabic text with multiple sections - Renders correctly
3. Hebrew + English mixed RTL/LTR - Renders correctly
4. Partial empty sections (only name or ref) - Handles gracefully

Checklist

• Confirmed no backports from Mapbox projects
• Changes described above
• Linked to issue Undefined text property for formatted text with multiple empty sections and right to left plugin #6444
• No visual changes (bug fix only)
• All existing tests pass (17 integration + 2476 unit)
• No public API changes
• CHANGELOG.md updated