[5.10] Change load to loadUnaligned

[ahoppen]

• Explanation: Same fix as load => loadUnaligned swift-package-manager#6929 since the code in swift-syntax is based on what is in SwiftPM. We cherry-picked this from main to package-release/509 but forgot to cherry-pick it to release/5.10
• Scope: This causes macro plugin crashes on Linux
• Risk: Low, we have had this change in the 509 release of swift-syntax and on main, just not on release/5.10
• Testing: We verified that this change fixed the issue in the 509 release and on main, it’s just missing on release/5.10
• Issue: n/a
• Reviewer: @bnbarham and @rintaro on load => loadUnaligned #2312

[ahoppen]

@swift-ci Please test

[rintaro]

Thank you🙏

[ahoppen]

@swift-ci Please test Windows

[vanvoorden]

Swift/UnsafeRawPointer.swift:440: Fatal error: load from misaligned raw pointer

Here is an extra breadcrumb trail if anyone else stumbles on this error building 510.0.0 on Linux.