Revert "[infra] Move commands from isolates to gen_tasks.go"

This reverts commit 66db75da67fb4c75207c2e495765e1e74584e3b1.

Reason for revert: Breaking PDFium/Flutter

Original change's description:
> [infra] Move commands from isolates to gen_tasks.go
> 
> This has the side effect of bundling recipes for all tasks,
> which will be required anyway to run recipes in the future.
> 
> Bug: skia:7050
> Change-Id: Ia30a95c750f2a237a8bf60263b2981682673c043
> Reviewed-on: https://skia-review.googlesource.com/81300
> Commit-Queue: Eric Boren <borenet@google.com>
> Reviewed-by: Kevin Lubick <kjlubick@google.com>

TBR=borenet@google.com,bungeman@google.com,rmistry@google.com,kjlubick@google.com

Change-Id: I38e00294f098ac91285a5cc464414654fc79a9e9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:7050
Reviewed-on: https://skia-review.googlesource.com/81741
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
39 files changed