Move defines to their own file
As described in
https://github.com/dwp-forge/columns/issues/5#issuecomment-
638467603
sometime the Lexer constants have not been (auto)loaded when a syntax plugin
is invoked (I'm not sure why).
In general PSR2 discourages a mix of main code and function/class setup
with the call to define() being considered main code.
This patch moves these the define calls to a separate new file, solving
both of the above problems.
These are not all our defines. Instead I focused on the ones that are
ENUM-like.
In the future we should think about what defines can be replaced by
class constants and what other define() calls should be moved.