refactor: snapshotting of runtime/ and cli/ (#21430)

This commit removes some of the technical debt related 
to snapshotting JS code:
- "cli/ops/mod.rs" and "cli/build.rs" no longer define "cli" extension
which was not required anymore
- Cargo features for "deno_runtime" crate have been unified in
"cli/Cargo.toml"
- "cli/build.rs" uses "deno_runtime::snapshot::create_runtime_snapshot"
API
instead of copy-pasting the code
- "cli/js/99_main.js" was completely removed as it's not necessary
anymore

Towards https://github.com/denoland/deno/issues/21137

cli/js/99_main.js

@@ -1,2 +0,0 @@
-// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
-import "ext:cli/runtime/js/99_main.js";