`mw.loadJsonData` in mw.lua throws an error if the input argument is
not a string. The error message should refer to the type of the input
argument `module`, not that of the variable `arg` (which is usually
undeclared, giving the type `nil`).
This also necessitates updating test `mw.loadJsonData, bad title (1)`
in CommonTests.lua, which checks for the error message if the input
is the number 0; the correct message should say "got number", not
"got nil".
Bug: T364987
Change-Id: I8362e91489a8ddc4c890e2799892f692c497c9b9
mw.loadData() allows for optimizing the loading Lua tables by requiring
only one parse and lookup. However it's often easier for people to
write/maintain bulk data in JSON rather than Lua tables.
mw.loadJsonData() has roughly the same characteristics as mw.loadData()
and it can be used on JSON content model pages in any namespace.
As noted on the linked bug report, it's possible to already implement
this by writing a wrapper Lua module that loads and parses the JSON
content. But that requires a dummy module for each JSON page, which is
just annoying and inconvenient.
Test cases are copied from the mw.loadData() ones, with a few omissions
for syntax not supported in JSON (e.g. NaN, infinity, etc.).
Bug: T217500
Change-Id: I1b35ad27a37b94064707bb8c9b7108c7078ed4d1
