Kernel: Add the /proc/stat ProcFS component

This exposes a small subset of the information exposed by the Linux
equivalent, and will be used to optimize applications that would like
to know the current CPU usage statistics, but don't want to read all of
the unrelated information in /proc/all

Kernel/GlobalProcessExposed.cpp

@@ -411,6 +411,29 @@ private:
     }
 };
 
+class ProcFSSystemStatistics final : public ProcFSGlobalInformation {
+public:
+    static NonnullRefPtr<ProcFSSystemStatistics> must_create();
+
+private:
+    ProcFSSystemStatistics();
+    virtual KResult try_generate(KBufferBuilder& builder) override
+    {
+        JsonObjectSerializer<KBufferBuilder> json { builder };
+        auto total_time_scheduled = Scheduler::get_total_time_scheduled();
+        json.add("total_time", total_time_scheduled.total);
+        json.add("kernel_time", total_time_scheduled.total_kernel);
+        json.add("user_time", total_time_scheduled.total - total_time_scheduled.total_kernel);
+        u64 idle_time = 0;
+        Processor::for_each([&](Processor& processor) {
+            idle_time += processor.time_spent_idle();
+        });
+        json.add("idle_time", idle_time);
+        json.finish();
+        return KSuccess;
+    }
+};
+
 class ProcFSOverallProcesses final : public ProcFSGlobalInformation {
 public:
     static NonnullRefPtr<ProcFSOverallProcesses> must_create();
@@ -730,6 +753,10 @@ UNMAP_AFTER_INIT NonnullRefPtr<ProcFSMemoryStatus> ProcFSMemoryStatus::must_crea
 {
     return adopt_ref_if_nonnull(new (nothrow) ProcFSMemoryStatus).release_nonnull();
 }
+UNMAP_AFTER_INIT NonnullRefPtr<ProcFSSystemStatistics> ProcFSSystemStatistics::must_create()
+{
+    return adopt_ref_if_nonnull(new (nothrow) ProcFSSystemStatistics).release_nonnull();
+}
 UNMAP_AFTER_INIT NonnullRefPtr<ProcFSOverallProcesses> ProcFSOverallProcesses::must_create()
 {
     return adopt_ref_if_nonnull(new (nothrow) ProcFSOverallProcesses).release_nonnull();
@@ -788,6 +815,10 @@ UNMAP_AFTER_INIT ProcFSMemoryStatus::ProcFSMemoryStatus()
     : ProcFSGlobalInformation("memstat"sv)
 {
 }
+UNMAP_AFTER_INIT ProcFSSystemStatistics::ProcFSSystemStatistics()
+    : ProcFSGlobalInformation("stat"sv)
+{
+}
 UNMAP_AFTER_INIT ProcFSOverallProcesses::ProcFSOverallProcesses()
     : ProcFSGlobalInformation("all"sv)
 {
@@ -854,6 +885,7 @@ UNMAP_AFTER_INIT NonnullRefPtr<ProcFSRootDirectory> ProcFSRootDirectory::must_cr
     directory->m_components.append(ProcFSSelfProcessDirectory::must_create());
     directory->m_components.append(ProcFSDiskUsage::must_create());
     directory->m_components.append(ProcFSMemoryStatus::must_create());
+    directory->m_components.append(ProcFSSystemStatistics::must_create());
     directory->m_components.append(ProcFSOverallProcesses::must_create());
     directory->m_components.append(ProcFSCPUInformation::must_create());
     directory->m_components.append(ProcFSDmesg::must_create());