Namespacing for fixity signatures (14032)

Namespace specifiers were added to syntax of fixity signatures:
  - sigdecl ::= infix prec ops | ...
  + sigdecl ::= infix prec namespace_spec ops | ...

To preserve namespace during renaming MiniFixityEnv type
now has separate FastStringEnv fields for names that should be
on the term level and for name that should be on the type level.

makeMiniFixityEnv function was changed to fill MiniFixityEnv in the right way:
 - signatures without namespace specifiers fill both fields
 - signatures with 'data' specifier fill data field only
 - signatures with 'type' specifier fill type field only

Was added helper function lookupMiniFixityEnv that takes care about
looking for a name in an appropriate namespace.

Updates haddock submodule.