Fix mscordbi metadata reader alignment bug on Linux. (dotnet/coreclr#19070)

Fix mscordbi metadata reader alignment bug on Linux. (dotnet/coreclr#19070)

Works fine on Windows minidumps, but on Linux (via OpenVirtualProcess
for production breakpoints and future core dumps) the compiler's struct
alignment rules are different. On Windows, classes/structs are aligned
based on the largest field. On Linux, they are 4 byte aligned regardless
of the field sizes.

https://github.com/dotnet/coreclr/issues/17692

Commit migrated from https://github.com/dotnet/coreclr/commit/e6ada167d7991b1ab6e1ea921c521a691610e269