[CMake] Fix dependencies for generating gparams_register_modules.cpp.

Previously CMake was not aware of which headers files the generation
of `gparams_register_modules.cpp` depended on. Consequently this could result
in broken incremental builds if

* Existing headers that declared module description/parameters change.
* New headers are added that declare module description/parameters.
* `.pyg` files that generate header files that declare module
  description/parameters change

Now the `z3_add_component()` CMake function has been modifed so that

* All header files that are generated from `.pyg` files are added as
dependencies and are scanned from module description/parameter
declarations. This implicit dependency of `gparams_register_modules.cpp`
depending on other generated header files seems unnecessary complex. We
should revisit this design decision once the Python/Makefile build
system is deprecated.

* The function now takes an optional `EXTRA_REGISTER_MODULE_HEADERS`
argument which allows the headers that declare module
description/paramters to be explicitly listed.

With this information CMake will now regenerate `gparams_register_modules.cpp`
correctly.

This required the `mk_gparams_register_modules_internal()` function to be
changed to take a list of header files rather than a list of component
source directories. The two consumers (CMake and Python/Makefile build
systems) of this function have been modified to work with this change.

This partially fixes #1030.

src/math/polynomial/CMakeLists.txt

@@ -11,5 +11,7 @@ z3_add_component(polynomial
     util
   PYG_FILES
     algebraic_params.pyg
+  EXTRA_REGISTER_MODULE_HEADERS
+    polynomial.h
 )