Add a standard string conversion for Civil type

[dinukaamarasinghe817]

Description:
Need to provide standards methods to convert a time:Civil value to a string value and a string value to a time:Civil value with utcOffset and timeAbbrev

Steps to reproduce:

1. Create a time:Civil value with a utcfOffset and a timeAbbrev
2. Convert the time:Civil value to a string using time:civilToString method
3. Conver the converted string value back to a time:Civil value using time:civilFromString method
4. Final value is not equivalent to the previous original value.

Affected modules

• Bal Persist for Redis DB : https://github.com/ballerina-platform/module-ballerinax-persist.redis

[TharmiganK]

Tried the following sample with the latest Ballerina version(2201.10.0) and it is working as expected:

public function main() returns error? {
    time:Civil civil1 = {
        year: 2022,
        month: 1,
        day: 29,
        hour: 22,
        minute: 48,
        second: 0,
        timeAbbrev: "Asia/Colombo",
        utcOffset: {hours: 5, minutes: 30}
    };
    string civilString = check time:civilToString(civil1);
    io:println("Civil Time string: ", civil1);
    time:Civil civil2 = check time:civilFromString(civilString);
    io:println("Civil Time 1: ", civil1);
    io:println("Civil Time 2: ", civil2);
}

$ bal run
Compiling source
        tharmigan/zone_bbe:0.1.0

Running executable

Civil Time string: {"utcOffset":{"hours":5,"minutes":30},"timeAbbrev":"Asia/Colombo","year":2022,"month":1,"day":29,"hour":22,"minute":48,"second":0}
Civil Time 1: {"utcOffset":{"hours":5,"minutes":30},"timeAbbrev":"Asia/Colombo","year":2022,"month":1,"day":29,"hour":22,"minute":48,"second":0}
Civil Time 2: {"utcOffset":{"hours":5,"minutes":30},"timeAbbrev":"+05:30","dayOfWeek":6,"year":2022,"month":1,"day":29,"hour":22,"minute":48}

This is fixed with #6986