This change takes all existing WebIDL files in the repo that had
definition lines without four leading spaces, and fixes them so they
have four leading spaces.
This follows on from the SVG linear gradients. It supports the same
features (xlink:href, gradientUnits, gradientTransform).
With this commit I have now implemented all web gradients :^)
(Though we are still missing a few parameters for SVG gradients,
e.g. spreadMethod).
