Kernel/Memory: Add option to annotate region mapping as immutable

We add this basic functionality to the Kernel so Userspace can request a
particular virtual memory mapping to be immutable. This will be useful
later on in the DynamicLoader code.

The annotation of a particular Kernel Region as immutable implies that
the following restrictions apply, so these features are prohibited:
- Changing the region's protection bits
- Unmapping the region
- Annotating the region with other virtual memory flags
- Applying further memory advises on the region
- Changing the region name
- Re-mapping the region

Kernel/API/VirtualMemoryAnnotations.h

@@ -14,6 +14,7 @@ namespace Kernel {
 enum class VirtualMemoryRangeFlags : u32 {
     None = 0,
     SyscallCode = 1 << 0,
+    Immutable = 1 << 1,
 };
 
 AK_ENUM_BITWISE_OPERATORS(VirtualMemoryRangeFlags);