fixed #12392. Tab indices now updated

[jonah-iden]

after deleting and moving a tab

What it does

Fixes #12392
updates tabs indeces of all tabs in a group when a tab is deleted or moved

How to test

as described in the issue

1. Open 4 editors
2. Close the second-to-last (third) tab
3. Close the last tab
4. no execption should be thrown anymore

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I still notice errors with this approach:

rpc-message-encoder.ts:184 Uncaught (in promise) Error: Tab close updated received for index 3 which does not exist
    at TabGroupExt.acceptTabOperation (/workspace/theia/packages/plugin-ext/lib/plugin/tabs.js:156:23)
    at TabsExtImpl.$acceptTabOperation (/workspace/theia/packages/plugin-ext/lib/plugin/tabs.js:286:27)
    at /workspace/theia/packages/plugin-ext/lib/common/proxy-handler.js:91:71
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async RpcProtocol.handleRequest (/workspace/theia/packages/core/lib/common/message-rpc/rpc-protocol.js:167:28)

Steps:

1. open 4 editors
2. close the third editor (2nd last)
3. close the last editor

[msujew]

I can't seem to reproduce the error any longer 👍

[vince-fugnitto]

I can confirm that the error is no longer reported in the console 👍

[tsmaeder]

@vince-fugnitto merge this one?