Handle import errors when simpleapi modules are imported without matplotlib installed (#39421)

By default, matplotlib is not installed when you install the Mantid Python library.
This will lead to import errors when attempting to access a module in the Framework,
as some of the algorithms use matplotlib. The solution here is to add dummy
functions that will raise an exception when called. This will delay the
exception handling from compile time to run time. Additionally, I added
a user prompt to notify the user to install matplotlib if they wish to
use these algorithms.

Fixes #39396. <!-- and fix #xxxx or close #xxxx xor resolves #xxxx. One
line per issue fixed. -->

### To test:
1- Build Mantid
2- In the conda environment, uninstall matplotlib "pip uninstall
matplotlib"
3- Run the following Python commands in the Python shell:
```
from mantid.simpleapi import plotSpectrum
plotSpectrum()
```
4- This will raise an exception and notify the user to install
matplotlib
5- Make sure other modules that doesn't depend on matplotlib works fine,
for example run:
```
from mantid.api import FrameworkManager
FrameworkManager.Instance()
```
6- It should work fine without errors as the FrameworkManager doesn't
require matplotlib


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Author: MohamedAlmaki

Framework/PythonInterface/mantid/simpleapi.py

@@ -50,10 +50,16 @@
 
 # register matplotlib projection
 try:
-    from mantid import plots  # noqa
-    from mantid.plots._compatability import plotSpectrum, plotBin  # noqa
+    from mantid import plots
+    from mantid.plots._compatability import plotSpectrum, plotBin
 except ImportError:
-    pass  # matplotlib is unavailable
+
+    def notSupported(*args, **kwargs):
+        raise ModuleNotFoundError("Plotting is not supported by default. Please install matplotlib to enable plotting.")
+
+    plots = notSupported
+    plotSpectrum = notSupported
+    plotBin = notSupported
 
 from mantid.kernel._aliases import *
 from mantid.api._aliases import *