Fix wrong mode on output for macros that shadow global macros

Fix wrong mode on output for macros that shadow global macros

Testcase: Define a math macro \AA, overriding the definition of \AA from
lib/symbols, then insert it in math mode.

* Before this commit: \text{\AA}, and \lyxmathsym{\AA} after deleting \text, but
  displayed like \AA.

* After this commit: \text{\AA} is inserted, but one gets \AA after deleting
  \text. The output is now consistent with the display and the meaning.

* Expected: only \AA is inserted. This is unfortuately not what one gets; for
  this to work, the scope of the macros would need to be resolved upon creating
  the inset.