Validate the startup parameters before opening files.

srv_start(): Renamed from innobase_start_or_create_for_mysql().
Move some of the validation to the caller, which is innobase_init().

innodb_log_buffer_size: Renamed from innobase_log_buffer_size,
using an unsigned type to avoid type casts.

innodb_log_file_size: Renamed from innobase_log_file_size,
using an unsigned type to avoid type casts.

innobase_read_io_threads, innobase_write_io_threads: Remove.
Directly map the startup parameters to the variables
srv_n_read_io_threads, srv_n_write_io_threads.

innodb_change_buffering: Renamed from innobase_change_buffering.
Use an integer type instead of a string.

innodb_flush_method: Renamed from innobase_file_flush_method.
Use an integer type instead of a string.

innodb_flush_method_names, innodb_flush_method_typelib: Valid values of
innodb_flush_method.

innodb_change_buffering_names, innodb_change_buffering_typelib:
Valid values of innodb_change_buffering.
Replaces innodb_change_buffering_names.

innodb_init(): Renamed from innobase_init().
innodb_init_abort(): Renamed from innobase_init_abort().

innodb_init(): When startup fails before opening files, do not call
innodb_init_abort(), but return 1 directly instead.

innodb_buffer_pool_size_init(): New function, to initialize
and normalize the buffer pool size and related parameters.

innodb_init_params(): New function, to check the startup parameters.

innodb_find_change_buffering_value(), innodb_change_buffering_validate(),
innodb_change_buffering_update(): Remove. These are made redundant by
innodb_change_buffering_typelib.

IBUF_USE_COUNT: Remove.

srv_normalize_init_values(): Remove. This will be done in innodb_init().

SysTablespace::normalize_size(): Renamed from SysTablespace::normalize().

RB: 8647
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
Reviewed-by: Mattias Jonsson <mattias.jonsson@oracle.com>