Kernel: Replace KResult and KResultOr<T> with Error and ErrorOr<T>

We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.

Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)

Kernel/KBufferBuilder.cpp

@@ -46,7 +46,7 @@ OwnPtr<KBuffer> KBufferBuilder::build()
     return move(m_buffer);
 }
 
-KResultOr<KBufferBuilder> KBufferBuilder::try_create()
+ErrorOr<KBufferBuilder> KBufferBuilder::try_create()
 {
     auto buffer = TRY(KBuffer::try_create_with_size(4 * MiB, Memory::Region::Access::ReadWrite));
     return KBufferBuilder { move(buffer) };
@@ -57,47 +57,47 @@ KBufferBuilder::KBufferBuilder(NonnullOwnPtr<KBuffer> buffer)
 {
 }
 
-KResult KBufferBuilder::append_bytes(ReadonlyBytes bytes)
+ErrorOr<void> KBufferBuilder::append_bytes(ReadonlyBytes bytes)
 {
     if (!check_expand(bytes.size()))
         return ENOMEM;
     memcpy(insertion_ptr(), bytes.data(), bytes.size());
     m_size += bytes.size();
-    return KSuccess;
+    return {};
 }
 
-KResult KBufferBuilder::append(const StringView& str)
+ErrorOr<void> KBufferBuilder::append(const StringView& str)
 {
     if (str.is_empty())
-        return KSuccess;
+        return {};
     if (!check_expand(str.length()))
         return ENOMEM;
     memcpy(insertion_ptr(), str.characters_without_null_termination(), str.length());
     m_size += str.length();
-    return KSuccess;
+    return {};
 }
 
-KResult KBufferBuilder::append(const char* characters, int length)
+ErrorOr<void> KBufferBuilder::append(const char* characters, int length)
 {
     if (!length)
-        return KSuccess;
+        return {};
     if (!check_expand(length))
         return ENOMEM;
     memcpy(insertion_ptr(), characters, length);
     m_size += length;
-    return KSuccess;
+    return {};
 }
 
-KResult KBufferBuilder::append(char ch)
+ErrorOr<void> KBufferBuilder::append(char ch)
 {
     if (!check_expand(1))
         return ENOMEM;
     insertion_ptr()[0] = ch;
     m_size += 1;
-    return KSuccess;
+    return {};
 }
 
-KResult KBufferBuilder::append_escaped_for_json(const StringView& string)
+ErrorOr<void> KBufferBuilder::append_escaped_for_json(const StringView& string)
 {
     for (auto ch : string) {
         switch (ch) {
@@ -123,7 +123,7 @@ KResult KBufferBuilder::append_escaped_for_json(const StringView& string)
                 TRY(append(ch));
         }
     }
-    return KSuccess;
+    return {};
 }
 
 }