[Master] Add the union of the types in the `Create variable with type` code action

[nipunayf]

Purpose

In scenarios like the one described in the sample, there may arise situations where dependent types require a union of types rather than individual ones. To address this, the PR introduces an additional code action with a union type alongside the existing ones to cover this specific use case.

Fixes #42591

Approach

Return the union of all the possible types along with the ones that are already provided in the respective code action.

Samples

https://github.com/ballerina-platform/ballerina-lang/assets/59343084/a8f874a2-b670-49bb-994f-b3b93fd37348

Check List

• [x] Read the Contributing Guide
• [ ] Updated Change Log
• [ ] Checked Tooling Support (#)
• [x] Added necessary tests
  • [x] 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