[CAS] Add llvm-cas tools to inspect on-disk LLVMCAS

[cachemeifyoucan]

Add a command-line tool llvm-cas to inspect the OnDisk CAS for
debugging purpose. It can be used to lookup/update ObjectStore or
put/get cache entries from ActionCache, together with other debugging
capabilities.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 38e5c8c7c5580224e0b3ae160491a0dcdf84490a ac0662b44cde12758c3e1be946651151938ee846 --extensions cpp -- llvm/tools/llvm-cas/llvm-cas.cpp

View the diff from clang-format here.

diff --git a/llvm/tools/llvm-cas/llvm-cas.cpp b/llvm/tools/llvm-cas/llvm-cas.cpp
index 291c6faf9f..b3dd0bb1f3 100644
--- a/llvm/tools/llvm-cas/llvm-cas.cpp
+++ b/llvm/tools/llvm-cas/llvm-cas.cpp
@@ -133,13 +133,12 @@ int main(int Argc, char **Argv) {
   return validateObject(*CAS, ID);
 }
 
-static Expected<std::unique_ptr<MemoryBuffer>>
-openBuffer(StringRef DataPath) {
+static Expected<std::unique_ptr<MemoryBuffer>> openBuffer(StringRef DataPath) {
   if (DataPath.empty())
     return createStringError(inconvertibleErrorCode(), "--data missing");
-  return errorOrToExpected(
-      DataPath == "-" ? llvm::MemoryBuffer::getSTDIN()
-                      : llvm::MemoryBuffer::getFile(DataPath));
+  return errorOrToExpected(DataPath == "-"
+                               ? llvm::MemoryBuffer::getSTDIN()
+                               : llvm::MemoryBuffer::getFile(DataPath));
 }
 
 int dump(ObjectStore &CAS) {