fix(i18n): globalstateservice stateupdates memory leak

[Bowen7]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• If applicable, have a visual design approval

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• clarity.design website / infrastructure changes
• Other... Please describe:

What is the current behavior?

Demo: https://stackblitz.com/edit/clarity-core-angularjs-yk53hdkf?file=src%2Findex.js

Continuously clicking the Show/Hide button, find that GlobalStateService.stateUpdates.subscriptions.length is continuously increasing:

10
15
20
25

And the detached cds-alert DOM in the memory is also increasing:

Affected components: which use @i8n, such as: alert, password...

Root Cause

core/projects/core/src/internal/decorators/i18n.ts

Line 61 in a93e9a6

protoOrDescriptor.__i18nSub = GlobalStateService.stateUpdates.subscribe(update => {

__i18nSub is on the protoOrDescriptor not the instance. Take alert as an example: all the alerts on the page will share the same __i18nSub, so if we remove all the alerts, only one __i18nSub(the newest one) will be unsubscribed. This causes the detached DOM to remain in memory.

There is also an issue that is caused by extends:
Assume that class A uses @i18n, and class B also uses @i18n while extending class A. In this case, an instance of class A will have two subscriptions when connectedCallback, but __i18nSub only saves the latest one. Therefore, only the latest subscription will be unsubscribed when disconnectedCallback.

So I added an if condition:

if (!this.__i18nSub) {

If we always use i18n as the name @i18n() i18n, it's okay, or do we need to keep these two subscriptions and unsubscribe from both of them when disconnectedCallback?

Issue Number: #67

What is the new behavior?

Unsubscribe from its subscription when the element is removed

Does this PR introduce a breaking change?

• Yes
• No

Other information

[github-actions]

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