Raise open file descriptors limit to avoid problem with pystack (mantidproject#40108)

### Description of work

The recent problems with running `pystack` in the error reporter have
been traced back to the fact that `pystack` was trying to open more file
descriptors than the limit set on most linux systems. A pr into
`pystack` has been made to improve their error messages
(bloomberg/pystack#260).

When this is a problem, you get a lot of this kind of output
```
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../.././libMantidJson.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../.././libMantidJson.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../.././libMantidJson.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../.././libMantidJson.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidTypes.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidTypes.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidTypes.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidTypes.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidPythonInterfaceCore.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidPythonInterfaceCore.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidPythonInterfaceCore.so
ERROR(process_core): Cannot open ELF file /home/bya67386/mambaforge/envs/test_htlp_links/lib/python3.11/site-packages/mantid/kernel/../../../../libMantidPythonInterfaceCore.
```

The issue started after the first new instrument view pr went in (this
commit
mantidproject@8733e98#diff-4a6d6571d2c59705d8a673667672de2d7dcc3c756c61a3f0195acdefac52fe34).
We're not that sure why, but it could be the addition of new libraries
such as `pyvista`.

This pr raises the limit (equivalent to `ulimit -n <value>`) for the
outer mantid process, which may eventually launch the error reporter.

### To test:

Package to test is at `mamba install
jhaigh0/label/raise_open_files_limit::mantidworkbench`

It would be good to test on idaaas where the core dump location is
already set up.
Run Segfault and check that the pystack output has been captured in the
stacktrace field.

Author: jhaigh0

qt/applications/workbench/workbench/app/start.py

@@ -9,7 +9,7 @@
 import subprocess
 import sys
 
-from mantid.kernel.environment import is_linux, is_windows
+from mantid.kernel.environment import is_linux
 from mantid.kernel import Logger
 
 if is_linux():
@@ -38,17 +38,28 @@ def start_error_reporter(workbench_pid):
     )
 
 
-def setup_core_dump_files():
+def _setup_core_dump_files():
     """
     This is done so that the error reporter can locate and read any core files produced.
     This allows us to recover traces from c++ based crashes.
     """
-    if is_linux():
-        try:
-            resource.setrlimit(resource.RLIMIT_CORE, (resource.RLIM_INFINITY, resource.getrlimit(resource.RLIMIT_CORE)[1]))
-        except ValueError as e:
-            log = Logger("Mantid Start")
-            log.warning(f"Problem when enabling core dumps\n{str(e)}")
+    try:
+        resource.setrlimit(resource.RLIMIT_CORE, (resource.RLIM_INFINITY, resource.getrlimit(resource.RLIMIT_CORE)[1]))
+    except ValueError as e:
+        log = Logger("Mantid Start")
+        log.warning(f"Problem when enabling core dumps\n{str(e)}")
+
+
+def _raise_open_file_descriptor_limit():
+    """
+    Done to avoid the limit being reached when running pystack in the error reporter
+    """
+    try:
+        nofile_max = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
+        resource.setrlimit(resource.RLIMIT_NOFILE, (nofile_max, nofile_max))
+    except ValueError as e:
+        log = Logger("Mantid Start")
+        log.warning(f"Problem when raising limit for number of open file descriptors\n{str(e)}")
 
 
 def start(options: argparse.ArgumentParser):
@@ -74,9 +85,10 @@ def start(options: argparse.ArgumentParser):
         if options.quit:
             launch_command += " --quit"
 
-        if not is_windows():
-            # preexec_fn is not supported on Windows
-            workbench_process = subprocess.Popen(launch_command, shell=True, preexec_fn=setup_core_dump_files)
+        if is_linux():
+            # currently, reading coredump files for error reports is only supported on linux
+            _raise_open_file_descriptor_limit()
+            workbench_process = subprocess.Popen(launch_command, shell=True, preexec_fn=_setup_core_dump_files)
         else:
             workbench_process = subprocess.Popen(launch_command, shell=True)