Fixes #24607.
This PR makes the logic that caches top level dependencies (things
present in import map) smarter, so we handle JSR dependencies without
root exports.
This commit adds "--serve" flag to "deno init" subcommand,
that provides a template for quick starting a project using
"deno serve".
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Co-authored-by: Asher Gomez <ashersaupingomez@gmail.com>