Move the `lines-of-code` tag from `py/summary/lines-of-code`.
Code Scanning will eventually look for this tag.
The intent is to treat the number of lines of user code for Python as the summary of
how much code was analysed, ignoring both external libraries and generated code.
This matches the current baseline metric the CodeQL Action computes for Python.
We'll revisit this decision, and the baseline, if necessary.
This is a proposed method for advertising which queries are measuring
the lines of code in a project in a more robust manner than inspecting
the rule id.
Note that the python "LinesOfUserCode" query should _not_ have this
property, as otherwise the results of the two queries will be summed.
