feat: check stylesheet, query, schematron attributes

[AirQuick]

When a wrong test type is specified, its error message is cryptic.

For example, specifying XSLT test type with a Schematron XSpec file:

C:\xspec>bin\xspec.bat -t tutorial\schematron\demo-01.xspec
Creating Test Stylesheet...


Running Tests...
Error on line 6 column 25 of demo-01-compiled.xsl:
  XTSE0210: The stylesheet module includes/imports itself directly or indirectly
...

This pull request errors out a bit more friendly:

C:\xspec>bin\xspec.bat -t tutorial\schematron\demo-01.xspec
Creating Test Stylesheet...

ERROR in x:description: Missing @stylesheet.
...