explicit exposure of MariaDB symbols for plugins

Currently the plugins have APIs they can use.

./include/mysql/plugin_function.h.pp
./include/mysql/plugin_audit.h.pp
./include/mysql/psi/psi_abi_v1.h.pp
./include/mysql/psi/psi_abi_v2.h.pp
./include/mysql/psi/psi_abi_v0.h.pp
./include/mysql/plugin_data_type.h.pp
./include/mysql/client_plugin.h.pp
./include/mysql/plugin_ftparser.h.pp
./include/mysql/plugin_auth.h.pp
./include/mysql/plugin_encryption.h.pp
./include/mysql/plugin_password_validation.h.pp

Mariadb doesn't restrict visibilty with -fvisisbility=hidden for general restriction of linking.
_attribute_((visibility("default"))) would define the symbols that are available for linking.

Provide a versioning of these exposed interfaces for ABI compatibility

Windows already uses __declspec(dllexport) under the define SERVICE_VERSION.