Add @pattern support for constraint package

[shafreenAnfar]

This was not implemented due to no support for Regex in the language.

#2850

[TharmiganK]

Required support issue : ballerina-platform/ballerina-spec#130

[TharmiganK]

The regex support is now given in the language : https://ballerina.io/spec/lang/master/#lang.regexp

Example usage for pattern matching :

import ballerina/io;

public function main() {
    // Defining a regular expression
    string:RegExp regExp = re `[0-9]*`;

    string testString1 = "0123456789";
    string testString2 = "012345ab";

    if regExp.isFullMatch(testString1) {
        io:println("Test string 1 is a full match");
    } else {
        io:println("Test string 1 is not a full match");
    }

    if regExp.isFullMatch(testString2) {
        io:println("Test string 2 is a full match");
    } else {
        io:println("Test string 2 is not a full match");
    }
}

Applying pattern constraint using the constraint module :

import ballerina/constraint;

string:RegExp regExp = re `[^0-9]*`;

@constraint:String {
    length: 10,
    pattern: regExp
}
type PhoneNumber string;

type User record {|
    string name;
    int age;
    @constraint:String {
        pattern: re `([0-9]{9}[v|V]|[0-9]{12})`
    }
    string nic;
    string address;
    PhoneNumber contactNumber;
|};

[TharmiganK]

Found a blocker in the runtime : ballerina-platform/ballerina-lang#38336