Move definition of search_joins attribute from records to search action

[cgunther]

Previously it was up to each record to define this attribute, if it
offered the search action. This created scenarios where a record like Bin
offered the search action, but didn't define the search_joins
attribute and therefore searching bins would error:

undefined method `search_joins=' for #<NetSuite::Records::Bin:0x00007f8f32948bf8 @internal_id="1044", @external_id=nil, @attributes={:bin_number=>"WIP-Fabric"}> (NoMethodError)

due to SearchResult assuming the record had such an attribute:

netsuite/lib/netsuite/support/search_result.rb

Line 112 in 9f10005

result_wrapper.search_joins = record

Now adding the search action to a record automatically adds the
necessary search_joins attribute.

The attribute was previously defined on AssemblyComponent,
SerializedInventoryItemLocation, and WorkOrderItem, however none of
those support actions at all, let alone the search action. They're all
records for sublist items. I suspect the attribute was erroneously
introduced in the first place as a result of copy/pasting to create the
record.

[cgunther]

This has been added piecemeal, record-by-record, in the past (#164, #280, #295, #334, #342, #349, #350, #412), but hopefully this now solves it once-and-for-all across all records, now and into the future.

[iloveitaly]

Much cleaner! Nice change.