[Dont merge - Breaking Change] Add helper function to preserve XML declaration as processing instruction

[chiranSachintha]

Purpose

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Fixes #

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Check List

• Read the Contributing Guide
• Updated Change Log
• Checked Tooling Support (#)
• Added necessary tests
  • Unit Tests
  • Spec Conformance Tests
  • Integration Tests
  • Ballerina By Example Tests
• Increased Test Coverage
• Added necessary documentation
  • API documentation
  • Module documentation in Module.md files
  • Ballerina By Examples

[chiranSachintha]

xml body = xml `<?xml version="1.1" encoding="UTF-8"?><A><B>123</B></A>`;

Here, we treated <?xml version="1.1" encoding="UTF-8"?> as a processing instruction. That’s why I created a processing instruction for it when parsing the XML stream. <?xml version="1.1" encoding="UTF-8"?> is actually a special type of processing instruction, it is XML declaration. We should create a separate type for this in the runtime. This can be considered as an improvement.

[gimantha]

This is a breaking change.

[codecov]

Codecov Report

❌ Patch coverage is 77.27273% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.28%. Comparing base (50805a9) to head (0bef29d).
⚠️ Report is 3 commits behind head on 2201.12.x.

Files with missing lines	Patch %	Lines
...ballerina/runtime/internal/xml/XmlTreeBuilder.java	72.22%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             2201.12.x   #44359   +/-   ##
============================================
  Coverage        77.28%   77.28%           
- Complexity       59163    59171    +8     
============================================
  Files             3541     3541           
  Lines           222660   222680   +20     
  Branches         28872    28879    +7     
============================================
+ Hits            172083   172106   +23     
+ Misses           40853    40850    -3     
  Partials          9724     9724           

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