Several `pthread_create(&sPlatformMainThread, ...` could be converted to `StartEventLoopTask`

[markus-becker-tridonic-com]

Problem

In a few code locations pthread_create(&sPlatformMainThread, ... is still used.

Proposed Solution

pthread_create(&sPlatformMainThread, ... could be converted to StartEventLoopTask according to https://github.com/project-chip/connectedhomeip/pull/11116#discussion_r739590362 as commented by @bzbarsky-apple.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[bzbarsky-apple]

There are no more pthread_create(&sPlatformMainThread, ... in the tree.