Allow more control over variable-naming syntax

[LN]

@Matthew_White

@LN, do you think it'd be possible to remove this restriction from XLSForms?

Agreed with @Xiphware that this is one of the important simplifications that makes XLSForms easier for users. I don't see any reason to remove it.

@Matthew_White

Perhaps XLSForm Offline uses the filename of the XLSForm as the name of the child node?

That is correct. There is a proposed change to always use data as other form converters do but it is a risky change and requires deeper review and testing: https://github.com/XLSForm/pyxform/pull/152. If someone has cycles to participate in that, it would be greatly appreciated.

@Matthew_White

Add an option in Collect under the Google Sheets settings to not add the name of the child node of the primary instance to column headers.

Some existing discussion of that at https://github.com/opendatakit/collect/issues/298 started by @Enrico_Ferreguti; see particularly this suggestion:

How about a configuration option in the Google Sheets settings such as
[ x ] Include form and group names in column names

By default, this would be checked and the behavior would be the same as it is now. If unchecked, only the field name would be included in the column headers.

A form with duplicate field names would not be able to be sent to Google Sheets.

Options 2-5 sound good to me. I would even be ok with simply warning in documentation and perhaps in the UI that column names in the output document may not be unique.