fix: avoid optimizing non-optimizable external deps

[bholmesdev]

Description

We discovered that Vite 3 will optimize deps added to ssr.noExternal, even when those deps are not optimizable. This change will check whether a dependency is optimizable before attempting to optimize.

• if you include a non-optimizable dep in ssr.noExternal 👉 don't optimize, don't log a warning
• if you include a non-optimizable dep in optimizeDeps.include 👉 don't optimize, DO log a warning

Additional context

• adds non-optimizable dependency to the optimize-deps playground test
• adds non-optimizable dependency to the ssr-deps playground test

☝️ Note: no unit tests were added to the .spec.ts files! This is because we're just checking whether your Vite config causes the test suite to bomb. By adding non-optimizable-dep to optimizeDeps.include, for example, we're implicitly checking whether Vite will (wrongly) attempt to optimize.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

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[patak-dev]

Thanks a lot @bholmesdev! Great explanation and test case too!
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