[Java 21] Support ballerina lang to build with Java 21

[warunalakshitha]

Purpose

Fixes #43119
Fixes #43146

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

[warunalakshitha]

We need to revisit spotbugs exclude for lang repository as a separate task later.

[HindujaB]

Shall we add the java21 branch to the PR build workflows?

[warunalakshitha]

Shall we add the java21 branch to the PR build workflows?

Added ubuntu and windows build. Full build pipeline will fail without stdlib migration. We can add that later.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 77.31%. Comparing base (1ffa817) to head (8f6d65d).
Report is 36 commits behind head on java21.

Files with missing lines	Patch %	Lines
...rc/main/java/io/ballerina/cli/cmd/CommandUtil.java	0.00%	1 Missing ⚠️
...rc/main/java/io/ballerina/cli/cmd/PushCommand.java	0.00%	1 Missing ⚠️
...debugadapter/evaluation/utils/EvaluationUtils.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             java21   #43087      +/-   ##
============================================
- Coverage     77.32%   77.31%   -0.01%     
+ Complexity    58537    58532       -5     
============================================
  Files          3460     3460              
  Lines        220048   220050       +2     
  Branches      28902    28902              
============================================
- Hits         170144   170133      -11     
- Misses        40491    40514      +23     
+ Partials       9413     9403      -10     

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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.

[gayaldassanayake]

Other than the comment added LGTM