add test case for gnumeric col width/row height import
add mock implementation for import_sheet_properties
add support for hidden col/row import from gnumeric
add hidden col/row import from XLSX
add test for xlsx hidden row/column import
column width is an optional attribute
use an exception to signal invalid xml files, fdo#63844
Let's not silently exit when exception is thrown. That's not very helpful.
First Excel 2003 XML file to play with.

Currently, parsing this file throws an exception, but we need to at
least be able to parse this format without throwing exceptions.
These functions don't have to be part of the template.
Put these global sax functions inside sax namespace.
This method is unused.
Add mechanism to parse arbitrary xml declarations.

With this, we can correctly parse <?mso-application ...?> tags.
Declaration may have multiple attributes.
No more declaration() handler callback.

The <?xml ?> declaration is also handled by the start_ and
end_declaration() callback pair.
Make sax_parser configurable.

The first item toggles whether the parser requires every xml stream
begins with <?xml...?> or not.
Add test for parsing custom declarations.

The test file is a simple Excel 2003 XML document.
Have dom_tree store multiple declaration attributes with names as keys.
Add unit test for parsing the xml declarations.
Share the xml parsing part.