refactor(core): cleanup feature flags for js source inclusion (#19463)

Remove `ExtensionFileSourceCode::LoadedFromFsDuringSnapshot` and feature
`include_js_for_snapshotting` since they leak paths that are only
applicable in this repo to embedders. Replace with feature
`exclude_js_sources`. Additionally the feature
`force_include_js_sources` allows negating it, if both features are set.
We need both of these because features are additive and there must be a
way of force including sources for snapshot creation while still having
the `exclude_js_sources` feature. `force_include_js_sources` is only set
for build deps, so sources are still excluded from the final binary.

You can also specify `force_include_js_sources` on any extension to
override the above features for that extension. Towards #19398.

But there was still the snapshot-from-snapshot situation where code
could be executed twice, I addressed that by making `mod_evaluate()` and
scripts like `core/01_core.js` behave idempotently. This allowed
unifying `ext::init_ops()` and `ext::init_ops_and_esm()` into
`ext::init()`.

runtime/examples/extension_with_ops/main.rs

@@ -28,7 +28,7 @@ async fn main() -> Result<(), AnyError> {
     PermissionsContainer::allow_all(),
     WorkerOptions {
       module_loader: Rc::new(FsModuleLoader),
-      extensions: vec![hello_runtime::init_ops()],
+      extensions: vec![hello_runtime::init()],
       ..Default::default()
     },
   );