SourceMap: Independent of settings.

<h5>SourceMap independence from settings</h5>

The aim is to make source-map generation
independent of WE's "generate .map" settings
for LESS and SCSS..

It will compile just once on document open (which
it already does); if the map generation is set,
read from the generated map file. Otherwise,
in compiler parameter we set path to temp file,
read all text and delete the file.

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<h5>Go To Definition:</h5>

In scenarios like `selector1 > selector2 + selector3`,
the CSS parser attach `+` and `>` signs to the prev
selector, while CSS source map count it with the
current node (SimpleSelector; part of selector).

This PR also fixes those scenarios for LESS.