[Language Server] Fix goto definition for single bal files

[NipunaRanasinghe]

Purpose

Fixes #15624.

Check List

• Read the Contributing Guide
• Required Balo version update
• 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-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@d0de7f1). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master   #15625   +/-   ##
=========================================
  Coverage          ?    6.25%           
  Complexity        ?     1579           
=========================================
  Files             ?     1395           
  Lines             ?    71137           
  Branches          ?     9188           
=========================================
  Hits              ?     4452           
  Misses            ?    66200           
  Partials          ?      485

Impacted Files	Coverage Δ	Complexity Δ
...alang/langserver/BallerinaTextDocumentService.java	0% <0%> (ø)	0 <0> (?)

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[nadeeshaan]

Looks good.