[Master] Improve diagnostic message when there is a union type in the select clause

[LakshanWeerasinghe]

Purpose

$subject

Fixes #40013

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

[pcnfernando]

Can you add few ambiguity tests as well

[LakshanWeerasinghe]

Added only single test since few of other tests are already found here

[codecov]

Codecov Report

Patch coverage: 58.72% and project coverage change: +0.01 🎉

Comparison is base (3542aa0) 76.43% compared to head (2aff8cd) 76.45%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #40642      +/-   ##
============================================
+ Coverage     76.43%   76.45%   +0.01%     
- Complexity    55210    55214       +4     
============================================
  Files          3380     3377       -3     
  Lines        208012   207977      -35     
  Branches      26918    26921       +3     
============================================
+ Hits         158995   158999       +4     
+ Misses        40272    40231      -41     
- Partials       8745     8747       +2     

Impacted Files	Coverage Δ
...erina/runtime/internal/BallerinaXmlSerializer.java	80.28% <0.00%> (ø)
.../ballerina/runtime/internal/TableOmDataSource.java	0.00% <0.00%> (ø)
...java/io/ballerina/runtime/internal/TableUtils.java	72.09% <0.00%> (ø)
...a/io/ballerina/runtime/internal/TypeConverter.java	67.32% <0.00%> (ø)
...java/io/ballerina/runtime/internal/XmlFactory.java	57.89% <0.00%> (ø)
...ternal/configurable/providers/cli/CliProvider.java	92.46% <ø> (ø)
...me/internal/configurable/providers/toml/Utils.java	85.45% <ø> (ø)
...ime/internal/diagnostics/RuntimeDiagnosticLog.java	100.00% <ø> (ø)
...allerina/runtime/internal/errors/ErrorReasons.java	100.00% <ø> (ø)
...llerina/runtime/internal/scheduling/Scheduler.java	77.92% <0.00%> (ø)
... and 115 more

... and 4 files with indirect coverage changes

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[github-actions]

This PR has been open for more than 15 days with no activity. This will be closed in 3 days unless the stale label is removed or commented.

[LakshanWeerasinghe]

Closing this PR since #40835 will address the things in this PR.