LibCpp: Add regression tests for the parser

For each .cpp file in the test suite data, there is a .ast file that
represents the "known good" baseline of the parser result.

Each .cpp file goes through the parser, and the result of
invoking `ASTNode::dump()` on the root node is compared to the
baseline to find regressions.

We also check that there were no parser errors when parsing the .cpp
files.

Meta/lint-clang-format.sh

@@ -13,7 +13,8 @@ if [ "$#" -eq "1" ]; then
             ':!:Base' \
             ':!:Kernel/FileSystem/ext2_fs.h' \
             ':!:Userland/Libraries/LibC/syslog.h' \
-            ':!:Userland/DevTools/HackStudio/LanguageServers/Cpp/Tests/*'
+            ':!:Userland/DevTools/HackStudio/LanguageServers/Cpp/Tests/*' \
+            ':!:Userland/Libraries/LibCpp/Tests/*'
     )
 else
     files=()