feat: support identifying jsxImportSource pragma dependencies

[kitsonk]

Ref: denoland/deno#8440

This PR adds the following features:

• parses out the @jsxImportSource pragma from a module
• adds the emitted module specifier as a dependency to the module
• Allows the loader trait to supply the specifier module, defaulting to jsx-runtime (this is needed because when specifying "dev" mode, the implicit module name changes to jsx-dev-runtime)

This, plus the concept of "imports" already in the graph should allow us to support the React 17 JSX transforms in CLI (and in theory Deploy) in the least "hacky" way possible.

For context, something like this:

/* @jsxImportSource https://esm.sh/preact */

export function A() {
  return <div>Hello Deno</div>;
}

will get emitted to something like this:

import { jsx as _jsx } from "https://esm.sh/preact/jsx-runtime";
/* @jsxImportSource https://esm.sh/preact */
export function A() {
    return _jsx("div", { children: "Hello Deno" }, void 0);
}

And the parsing of the module would identify that https://esm.sh/preact/jsx-runtime would be what would be a runtime dependency and adds it to the dependencies of the graph module.

[dsherret]

LGTM

[dsherret]

LGTM