Update directory structure and package names

[aashikam]

Purpose

Related to ballerina-platform/ballerina-library#1623

Checklist

• Linked to an issue
• Updated the changelog
• Added tests

[codecov]

Codecov Report

Merging #186 (2496ead) into main (8ee6cea) will not change coverage.
The diff coverage is 90.90%.

@@            Coverage Diff            @@
##               main     #186   +/-   ##
=========================================
  Coverage     80.32%   80.32%           
  Complexity       96       96           
=========================================
  Files            26       26           
  Lines           615      615           
  Branches         60       60           
=========================================
  Hits            494      494           
  Misses           87       87           
  Partials         34       34           

Impacted Files	Coverage Δ
ballerina/annotation.bal	100.00% <ø> (ø)
ballerina/caller.bal	100.00% <ø> (ø)
ballerina/client.bal	100.00% <ø> (ø)
ballerina/config.bal	90.90% <ø> (ø)
ballerina/init.bal	100.00% <ø> (ø)
ballerina/listener.bal	100.00% <ø> (ø)
ballerina/message.bal	100.00% <ø> (ø)
.../stan/BallerinaNatsStreamingConnectionFactory.java	87.80% <ø> (ø)
.../main/java/io/ballerina/stdlib/stan/Constants.java	100.00% <ø> (ø)
.../src/main/java/io/ballerina/stdlib/stan/Utils.java	88.88% <ø> (ø)
... and 16 more

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