refactor: move JSValue.get to JSObject

[DonIsaac]

What does this PR do?

part of #15141

This lets us leverage the type system to only call .get on known JSObjects.

How did you verify your code works?

Existing tests cover all changes.

[robobun]

^{Updated 6:48 PM PT - Mar 2nd, 2025}

❌ @DonIsaac, your commit 4b30526 has 3 failures in Build #12588:

• test/js/web/fetch/fetch.test.ts - 1 failing on 🍎 14 aarch64
• test/cli/install/bun-install-registry.test.ts - 1 failing on 🪟 2019 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🪟 2019 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🪟 2019 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🍎 14 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🍎 13 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 12 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 20.04 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 24.04 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 22.04 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 3.20 aarch64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🍎 14 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 24.04 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 22.04 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 12 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 20.04 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 20.04 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 22.04 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 24.04 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🍎 13 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 12 x64
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 3.20 x64-baseline
• test/js/third_party/stripe/stripe.test.ts - 1 failing on 🐧 3.20 x64

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🧪   try this PR locally:

bunx bun-pr 17865