[Transformer] Order Variables section

[bhirsz]

Robot style guide recommends ordering the variables based in their complexity: https://docs.robotframework.org/docs/style_guide/guide#variables

[bhirsz]

Transformer should be optional for now.
It should also sort in alpthabetical order (and respecting 1 -> 2 ->10). It should first sort by complexity, then by name, Both should be configurable (enable/disable sorting by complexity or by name flags).

[bhirsz]

Whitespace and comments should be preserved - same as OrderSettingsSection.

Disablers should be respected.

Order by type (scalad/list/dict) will not be supported but could be added in the future.