There is no need to use shell here, and we should not assume that user's
zshrc configures the PATH correctly. Instead, we should use the
`Process` API to run commands directly, and assume that the PATH in the
process spawn environment is correctly configured.

The change adds a conditional import excluding the JavaScriptEventLoop module that's not yet fully compatible with Embedded Swift. With the `JSObject` type from the JavaScriptKit dependency, which is also now compatible with Embedded Swift, record types are now mapped to `JSObject`. As for fields marked as optional in originating IDL, these are now correctly mapped as optional in Swift.

This changes improves compatibility of the WebAPIKit library with Embedded Swift. Unsupported concurrency code is excluded when concurrency is not available, including the use of async sequences. Use of closure patterns is cleaned up to use getters and setters directly instead of property wrappers, which reduces binary code size when Embedded Swift is used.

This change fixes an issue with the use of property wrappers for closures in WebAPIKit, which caused unnecessary increases in binary code size for products utilizing this library. Use of property wrappers is removed and simple direct getter and setter accessors are used for properties of closure types instead.