[lldb] const a couple of getters on MemoryRegionInfo

[DavidSpickett]

Summary

GetDirtyPageList was being assigned to const & in most places anyway.
If you wanted to change the list you'd make a new one and call
SetDirtyPageList.

GetPageSize is just an int so no issues being const.

[DavidSpickett]

Landed as obvious as I'll shortly land the follow up.

lldb/include/lldb/Target/MemoryRegionInfo.h

return m_range == rhs.m_range && m_read == rhs.m_read &&
            m_is_stack_memory == rhs.m_is_stack_memory;
   }
 
   bool operator!=(const MemoryRegionInfo &rhs) const { return !(*this == rhs); }
 
   /// Get the target system's VM page size in bytes.
   /// \return
   ///     0 is returned if this information is unavailable.
-  int GetPageSize() { return m_pagesize; }
+  int GetPageSize() const { return m_pagesize; }
 
   /// Get a vector of target VM pages that are dirty -- that have been
   /// modified -- within this memory region.  This is an Optional return
   /// value; it will only be available if the remote stub was able to
   /// detail this.
-  llvm::Optional<std::vector<lldb::addr_t>> &GetDirtyPageList() {
+  const llvm::Optional<std::vector<lldb::addr_t>> &GetDirtyPageList() const {
     return m_dirty_pages;
   }
 
   OptionalBool IsStackMemory() const { return m_is_stack_memory; }
 
   void SetIsStackMemory(OptionalBool val) { m_is_stack_memory = val; }
 
   void SetPageSize(int pagesize) { m_pagesize = pagesize; }

lldb/source/API/SBMemoryRegionInfo.cpp

bool SBMemoryRegionInfo::HasDirtyMemoryPageList() {
 
   return m_opaque_up->GetDirtyPageList().hasValue();
 }
 
 uint32_t SBMemoryRegionInfo::GetNumDirtyPages() {
   LLDB_INSTRUMENT_VA(this);
 
   uint32_t num_dirty_pages = 0;
-  llvm::Optional<std::vector<addr_t>> dirty_page_list =
+  const llvm::Optional<std::vector<addr_t>> &dirty_page_list =
       m_opaque_up->GetDirtyPageList();
   if (dirty_page_list.hasValue())
     num_dirty_pages = dirty_page_list.getValue().size();
 
   return num_dirty_pages;
 }
 
 addr_t SBMemoryRegionInfo::GetDirtyPageAddressAtIndex(uint32_t idx) {