[NOT READY] [v2] Lazily initialize built-in plugins to reduce command execution time

[aemous]

Issue #, if available:

• Contributes to AWS CLI slow startup #9011.

Notes:

• This PR is a merge of a staging branch for the lazy plugin initialization project. All commits in this PR are from PRs that have already been reviewed and approved. The following PRs are in-scope for this merge PR:
  • [v2] Implement LazyCommand for deferring modules until their commands are invoked, and make PrefixTrie public #10299
  • [v2] Implement event handlers registry for built-in plugins #10305
  • [v2] Implement LazyInitEmitter for deferred plugin-loading #10343
  • [v2] Implement lazy plugin initialization #10356

Description of changes:

• Switch from eagerly importing and initializing all built-in plugins eagerly to lazy-loading them when relevant events are emitted, command(s) are invoked, or help docs are generated.

Description of tests:

• Successfully ran pre-production build workflow (see Build Internal GitHub Action).

Benchmarking data:

• TODO describe benchmarking method and results, with and without this patch.

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