Set OpenSSL SHA1 flag in build scripts

[siegfriedpammer]

Summary

• Set OPENSSL_ENABLE_SHA1_SIGNATURES=1 directly in restore, build, update-deps, clean, publish, local publish, and format scripts before they invoke dotnet or the formatter hook.
• Export the same variable in the pre-commit formatter hook for direct hook usage.

Verification

• env -u OPENSSL_ENABLE_SHA1_SIGNATURES pwsh ./build.ps1 -Configuration Debug --no-restore
• env -u OPENSSL_ENABLE_SHA1_SIGNATURES pwsh ./BuildTools/format.ps1
• git diff --check origin/master...HEAD