[vm] Decouple assemblers from runtime.

This is the next step towards preventing compiler from directly peeking
into runtime and instead interact with runtime through a well defined
surface. The goal of the refactoring to locate all places where compiler
accesses some runtime information and partion those accesses into two
categories:

- creating objects in the host runtime (e.g. allocating strings, numbers, etc)
during compilation;
- accessing properties of the target runtime (e.g. offsets of fields) to
embed those into the generated code;

This change introduces dart::compiler and dart::compiler::target namespaces.

All code in the compiler will gradually be moved into dart::compiler namespace.
One of the motivations for this change is to be able to prevent access to
globally defined host constants like kWordSize by shadowing them in the
dart::compiler namespace.

The nested namespace dart::compiler::target hosts all information about
target runtime that compiler could access, e.g. compiler::target::kWordSize
defines word size of the target which will eventually be made different
from the host kWordSize (defined by dart::kWordSize).

The API for compiler to runtime interaction is placed into compiler_api.h.

Note that we still permit runtime to access compiler internals directly -
this is not going to be decoupled as part of this work.

Issue https://github.com/dart-lang/sdk/issues/31709

Change-Id: If4396d295879391becfa6c38d4802bbff81f5b20
Reviewed-on: https://dart-review.googlesource.com/c/90242
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

runtime/vm/stack_frame.h

@@ -6,6 +6,7 @@
 #define RUNTIME_VM_STACK_FRAME_H_
 
 #include "vm/allocation.h"
+#include "vm/frame_layout.h"
 #include "vm/interpreter.h"
 #include "vm/object.h"
 #include "vm/stack_frame_kbc.h"
@@ -32,61 +33,6 @@ class ObjectPointerVisitor;
 class RawContext;
 class LocalVariable;
 
-struct FrameLayout {
-  // The offset (in words) from FP to the first object.
-  int first_object_from_fp;
-
-  // The offset (in words) from FP to the last fixed object.
-  int last_fixed_object_from_fp;
-
-  // The offset (in words) from FP to the first local.
-  int param_end_from_fp;
-
-  // The offset (in words) from FP to the first local.
-  int first_local_from_fp;
-
-  // The fixed size of the frame.
-  int dart_fixed_frame_size;
-
-  // The offset (in words) from FP to the saved pool (if applicable).
-  int saved_caller_pp_from_fp;
-
-  // The offset (in words) from FP to the code object (if applicable).
-  int code_from_fp;
-
-  // The number of fixed slots below the saved PC.
-  int saved_below_pc() const { return -first_local_from_fp; }
-
-  // Returns the FP-relative index where [variable] can be found (assumes
-  // [variable] is not captured), in words.
-  int FrameSlotForVariable(const LocalVariable* variable) const;
-
-  // Returns the FP-relative index where [variable_index] can be found (assumes
-  // [variable_index] comes from a [LocalVariable::index()], which is not
-  // captured).
-  int FrameSlotForVariableIndex(int index) const;
-
-  // Returns the FP-relative index where [variable] can be found (assumes
-  // [variable] is not captured), in bytes.
-  int FrameOffsetInBytesForVariable(const LocalVariable* variable) const {
-    return FrameSlotForVariable(variable) * kWordSize;
-  }
-
-  // Returns the variable index from a FP-relative index.
-  intptr_t VariableIndexForFrameSlot(intptr_t frame_slot) const {
-    if (frame_slot <= first_local_from_fp) {
-      return frame_slot - first_local_from_fp;
-    } else {
-      ASSERT(frame_slot > param_end_from_fp);
-      return frame_slot - param_end_from_fp;
-    }
-  }
-
-  // Called to initialize the stack frame layout during startup.
-  static void Init();
-};
-
-extern FrameLayout compiler_frame_layout;
 extern FrameLayout runtime_frame_layout;
 
 // Generic stack frame.