Resolving two build issues

Switches coveralls to coverage, since we have not used coveralls since
2018.
Additionally, we've added gcov tooling support as both an automatic
target, and manual instructions.

The rest of the diff is changing coveralls into coverage

As a first step for switching from TCMalloc to JEMalloc as the custom
memory allocator, this commit removes every instance of the flag
TCMALLOC_LIBRARIES_LINKTIME in all the CMakeList.txt files. This flag
was never used by the code, so this commit is invisible project-wise.

Apply change to insert export macros into class definition using cmake GenerateExportHeader
feature to 3 more projects: API, Crystal and CurveFitting
Have replaced DllExport with the cmake macro except in these places:

a) class templates - the definitions of class template member functions need to be in the
same unit as the declaration so dllimport gives a compilation error in the client code
(C2491 in VS) eg SingleValueParameter, SingleValueParameterParser
b) headers which are in a project but aren't included by any .cpp units in the project
eg IBackgroundFunction.h, ICatalogInfoService.h. In these cases I've removed the DLLExport
attribute completely

For the API target there were a couple of special cases\extras:

API has some conditional use of the extern keyword to control instantiation of template
classes. This has been inserted into the automatically created dllconfig.h using a cmake
switch that allows some custom content to be appended to the end of the file. Few of the
targets require this so I've added a boolean parameter to the wrapper function to handle
this GENERATE_MANTID_EXPORT_HEADER

I also had to add explicit include directories to PythonInterfaceCore where it imports an
API target header (in the unit ExtractWorkspace.h) without having API as a dependency

The OpenMP macros have to check the ConfigService for
the number of threads and then set it in a parallel region
or new threads using OpenMP do not see the changed value.
Any libraries using OpenMP therefore need to link to Kernel
for ConfigService.

Re #27061

Dependencies now go into Frameworks as seems to be done for
other application bundles. This should bring us close to
be able to sign the app bundle

Use macOS over OSX to refer to system.
Remove old OSX version workarounds
Refs #26261

Co-Authored-By: alicerussell1 <46603316+alicerussell1@users.noreply.github.com>

The code is used in multiple places. This refactor allows for
easier reuse.

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This reverts commit ac2d7a0c.

comment out "INSTALL_RPATH"-related cmake commands from "Framework" subfolders

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This allows the iterator functions to be inlined

Also added performances tests.
Refs #17913

Refs #17913