[master][LS] Fix IndexOutOfBoundException in STModify API

[NipunaRanasinghe]

Purpose

$subject.

Fixes wso2/product-ballerina-integrator#135

Duplicate of #43976 for the master branch

Approach

Describe how you are implementing the solutions along with the design details.

Samples

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Remarks

List any other known issues, related PRs, TODO items, or any other notes related to the PR.

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

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 14 lines in your changes missing coverage. Please review.

Please upload report for BASE (pr-merge@0d78644). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ns/ballerina/document/BallerinaTreeModifyUtil.java	50.00%	9 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             pr-merge   #44047   +/-   ##
===========================================
  Coverage            ?   75.07%           
  Complexity          ?    57570           
===========================================
  Files               ?     3541           
  Lines               ?   222541           
  Branches            ?    28857           
===========================================
  Hits                ?   167070           
  Misses              ?    46194           
  Partials            ?     9277           

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