Fix not showing empty lines in the code snippets in the description

[NipunaMadhushan]

Purpose

$subject

Fixes #38963

Approach

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

Samples

Provide high-level details about the samples related to this feature.

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

[chiranSachintha]

doc.append(codeLineNode.codeDescription().toString().isEmpty() ? "\n" codeLineNode.codeDescription().toString());

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 75.06%. Comparing base (d6b4583) to head (f653ae5).
Report is 495 commits behind head on master.

Files with missing lines	Patch %	Lines
.../main/java/org/ballerinalang/docgen/Generator.java	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #43786      +/-   ##
============================================
- Coverage     77.40%   75.06%   -2.34%     
+ Complexity    58626    57557    -1069     
============================================
  Files          3446     3541      +95     
  Lines        219216   222534    +3318     
  Branches      28975    28857     -118     
============================================
- Hits         169680   167047    -2633     
- Misses        40101    46208    +6107     
+ Partials       9435     9279     -156     

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