Unify object method scope and object field scope

[rdhananjaya]

Purpose

With this change, we can extract out object methods as standalone functions, the receiver will be stored as a closure variable.

class A {
    int i = 0;
    function foo(int i) returns int {
        returns self.i + i;
    }
}

A a = new();
function (int) returns int bar = a.foo;
int i = bar(1);

Fixes #25769

Approach

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Samples

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Remarks

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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

[hasithaa]

Looks good to me.