Tooling support for isolated functions

[MaryamZi]

Description:
isolated functions will be introduced with #25761.

With this, the isolated qualifier can be used with functions, object methods, service resources, etc.

e.g.,

isolated function foo() {
}

#25763 will add it for function type descriptors and anonymous functions.

Lang issue - #24907

[nadeeshaan]

Fixed in latest master. Hence closing the issue