Use convert API and enable disabled tests

[Nadeeshan96]

Purpose

$title
Partially fixes the issue ballerina-platform/ballerina-library#3933

Examples

Checklist

• Linked to an issue
• Updated the changelog
• Added tests
• Updated the spec
• Checked native-image compatibility

[codecov]

Codecov Report

Patch coverage: 85.71% and project coverage change: -0.04 ⚠️

Comparison is base (4f51feb) 81.60% compared to head (b63cfd7) 81.57%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1545      +/-   ##
============================================
- Coverage     81.60%   81.57%   -0.04%     
  Complexity      524      524              
============================================
  Files           388      388              
  Lines         21064    21060       -4     
  Branches       4702     4700       -2     
============================================
- Hits          17189    17179      -10     
- Misses         2892     2898       +6     
  Partials        983      983              

Impacted Files	Coverage Δ
.../stdlib/http/api/service/signature/ParamUtils.java	83.87% <50.00%> (ø)
...lib/http/api/service/signature/AllQueryParams.java	90.76% <100.00%> (-0.28%)	⬇️
.../service/signature/builder/JsonPayloadBuilder.java	90.90% <100.00%> (-1.40%)	⬇️
...ice/signature/converter/JsonToRecordConverter.java	64.70% <100.00%> (-11.77%)	⬇️

... and 3 files with indirect coverage changes

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[TharmiganK]

LGTM