ODS: provide a flag to skip generation of default build methods

Some operations need to override the default behavior of builders, in
particular region-holding operations such as affine.for or tf.graph want to
inject default terminators into the region upon construction, which default
builders won't do.  Provide a flag that disables the generation of default
builders so that the custom builders could use the same function signatures.
This is an intentionally low-level and heavy-weight feature that requires the
entire builder to be implemented, and it should be used sparingly.  Injecting
code into the end of a default builder would depend on the naming scheme of the
default builder arguments that is not visible in the ODS.  Checking that the
signature of a custom builder conflicts with that of a default builder to
prevent emission would require teaching ODG to differentiate between types and
(optional) argument names in the generated C++ code.  If this flag ends up
being used a lot, we should consider adding traits that inject specific code
into the default builder.

PiperOrigin-RevId: 256640069