[Improvement]: Improve the error reporting of XML templates when used as key values in tables

[nipunayf]

Description

The current implementation only considers and simply checks if the XML expression generates an XML element or text, returning true without considering whether the interpolated expressions are constant or not.

ballerina-lang/compiler/ballerina-lang/src/main/java/org/wso2/ballerinalang/compiler/semantics/analyzer/TypeChecker.java

Lines 1526 to 1527 in 42c4311

	case XML_ELEMENT_LITERAL:
	case XML_TEXT_LITERAL:

Describe your problem(s)

No response

Describe your solution(s)

This implementation should be improved to consider the following types of XML subtypes along with checking the expressions nested within them.

1. xml Element
2. xml Comment
3. xml ProcessingInstruction
4. xml Text
5. xml Sequence

Related area

-> Compilation

Related issue(s) (optional)

#13944

Suggested label(s) (optional)

No response

Suggested assignee(s) (optional)

No response

[nipunayf]

Currently, the issue is blocked by #41981