externals: Add catch2 v3.2.1

Merge commit '6879e5bb1c' as 'externals/catch'

externals/catch/tools/scripts/buildAndTest.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env sh
+
+# Start at the root of the Catch project directory, for example:
+# cd Catch2
+
+# begin-snippet: catch2-build-and-test
+# 1. Regenerate the amalgamated distribution
+./tools/scripts/generateAmalgamatedFiles.py
+
+# 2. Configure the full test build
+cmake -Bdebug-build -H. -DCMAKE_BUILD_TYPE=Debug -DCATCH_DEVELOPMENT_BUILD=ON -DCATCH_BUILD_EXAMPLES=ON -DCATCH_BUILD_EXTRA_TESTS=ON -DCATCH_ENABLE_CONFIGURE_TESTS=ON
+
+# 3. Run the actual build
+cmake --build debug-build
+
+# 4. Run the tests using CTest
+cd debug-build
+ctest -j 4 --output-on-failure -C Debug
+# end-snippet