Target::ReadMemory read from read-only binary file Section, not memory

Commiting this patch for Augusto Noronha who is getting set
up still.

This patch changes Target::ReadMemory so the default behavior
when a read is in a Section that is read-only is to fetch the
data from the local binary image, instead of reading it from
memory.  Update all callers to use their old preferences
(the old prefer_file_cache bool) using the new API; we should
revisit these calls and see if they really intend to read
live memory, or if reading from a read-only Section would be
equivalent and important for performance-sensitive cases.

rdar://30634422

Differential revision: https://reviews.llvm.org/D100338

lldb/source/Target/ThreadPlanStepRange.cpp

@@ -264,10 +264,9 @@ InstructionList *ThreadPlanStepRange::GetInstructionsForAddress(
         // Disassemble the address range given:
         const char *plugin_name = nullptr;
         const char *flavor = nullptr;
-        const bool prefer_file_cache = true;
         m_instruction_ranges[i] = Disassembler::DisassembleRange(
             GetTarget().GetArchitecture(), plugin_name, flavor, GetTarget(),
-            m_address_ranges[i], prefer_file_cache);
+            m_address_ranges[i]);
       }
       if (!m_instruction_ranges[i])
         return nullptr;