Update and refactor ballerina/encoding module APIs

[ldclakmal]

Need to update and refactor ballerina/encoding module APIs for Swan Lake
https://docs.google.com/spreadsheets/d/1PyMAlAvgkEL0RpW8CVUj1ccW_61Vm6SMbvadFVYRpSA/edit?usp=sharing

[ldclakmal]

It is decided to rename 'encoding' package to 'url' package for Swan Lake release.

Currently, the ballerina/encoding package has only 4 APIs for encoding/decoding URLs. The base16/64 encoding/decoding APIs were introduced to langlib sometime ago and it was decided to remove those APIs from ballerina/encoding module [1] [2]. The mime related encoding/decoding APIs are in ballerina/mime module [3].

public function encodeBase64Url(byte[] input) returns string {}
public function decodeBase64Url(string input) returns byte[]|Error {}
public function encodeUriComponent(string uriComponent, string charset) returns string|Error {}
public function decodeUriComponent(string uriComponent, string charset) returns string|Error {}

Since it is no longer needed to have a separate encoding package only for these APIs, we will be renaming the package as ballerina/url for Swan Lake release onwards. The updated APIs would be:

public function base64Encode(byte[] input) returns string {}
public function base64Decode(string input) returns byte[]|Error {}
public function encode(string url, string charset) returns string|Error {}
public function decode(string url, string charset) returns string|Error {}

[1] ballerina-platform/ballerina-spec#314
[2] https://groups.google.com/g/ballerina-dev/c/sbASEwIl44k/m/0YlP3IcXFwAJ
[3] https://ballerina.io/learn/api-docs/ballerina/#/ballerina/mime/1.0.6/mime/functions

[ldclakmal]

The usage of first 2 APIs is only by ballerina/jwt module and it was decided to move those to ballerina/jwt module as internal functions. The best place to keep second 2 APIs are ballerina/http and it was decided to move those to ballerina/http module.
Finally, we will remove ballerina/encoding module from standard libraries with Swan Lake Alpha 3.

[ldclakmal]

It was decided to rename the module as ballerina/url and keep the following 2 APIs.

public function encode(string str, string charset) returns string|Error {}
public function decode(string str, string charset) returns string|Error {}