Warnings logged by the operation block macro lack context

[ahus1]

I'm backporting a change that I applied in the IntelliJ AsciiDoc plugin to highlight problems with the operation macro in the editor.

When using logger.warn with a cursor the output contains the file and line number where the problem occurred.

The unit tests will log an example output like this (from a unit test)

WARNING: <stdin>: line 1: Snippet missing-snippet not found at C:\Users\...\AppData\Local\Temp\junit8239829976219138844\gradle-project\build\generated-snippets/some-operation/missing-snippet.adoc for operation some-operation

[wilkinsona]

Thanks very much, @ahus1.