[vm/isolates] Introduce fast isolate spawn in AOT.

Speed up is achieved by sharing most of the dart code, object store
and class table between isolates in single isolate group. So
instead of bootstrapping isolate from the snapshot, isolate is
initialized by setting pointers to existing data structures already
set up for first isolate, and only few isolate-specific structures (moved
to newly introducted isolate_object_store) are created.

To allow for safe cross-isolate switchable call site, type test cache
mutations additional synchronization via RunWithStoppedMutators(that
relies on safepoints) was added.
Besides switchable call sites, no other mutation to the dart code is
done in AOT, which allows such sharing.

Bug: dart-lang#37835
Bug: dart-lang#36097
Change-Id: I64c86525f4ef9cb30567a49a106bfe700355942b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136780
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

Author: aam

assembler_arm.cc

@@ -2004,8 +2004,7 @@ void Assembler::LoadClassId(Register result, Register object, Condition cond) {
 void Assembler::LoadClassById(Register result, Register class_id) {
   ASSERT(result != class_id);
 
-  const intptr_t table_offset = target::Isolate::class_table_offset() +
-                                target::ClassTable::table_offset();
+  const intptr_t table_offset = target::Isolate::class_table_table_offset();
 
   LoadIsolate(result);
   LoadFromOffset(kWord, result, result, table_offset);
@@ -3529,8 +3528,7 @@ void Assembler::LoadAllocationStatsAddress(Register dest, intptr_t cid) {
   ASSERT(cid > 0);
 
   const intptr_t shared_table_offset =
-      target::Isolate::class_table_offset() +
-      target::ClassTable::shared_class_table_offset();
+      target::Isolate::shared_class_table_offset();
   const intptr_t table_offset =
       target::SharedClassTable::class_heap_stats_table_offset();
   const intptr_t class_offset = target::ClassTable::ClassOffsetFor(cid);

assembler_arm64.cc

@@ -1155,8 +1155,7 @@ void Assembler::LoadClassId(Register result, Register object) {
 void Assembler::LoadClassById(Register result, Register class_id) {
   ASSERT(result != class_id);
 
-  const intptr_t table_offset = target::Isolate::class_table_offset() +
-                                target::ClassTable::table_offset();
+  const intptr_t table_offset = target::Isolate::class_table_table_offset();
 
   LoadIsolate(result);
   LoadFromOffset(result, result, table_offset);
@@ -1631,8 +1630,7 @@ void Assembler::MaybeTraceAllocation(intptr_t cid,
   ASSERT(cid > 0);
 
   const intptr_t shared_table_offset =
-      target::Isolate::class_table_offset() +
-      target::ClassTable::shared_class_table_offset();
+      target::Isolate::shared_class_table_offset();
   const intptr_t table_offset =
       target::SharedClassTable::class_heap_stats_table_offset();
   const intptr_t class_offset = target::ClassTable::ClassOffsetFor(cid);

assembler_ia32.cc

@@ -2409,8 +2409,7 @@ void Assembler::MaybeTraceAllocation(intptr_t cid,
   Address state_address(kNoRegister, 0);
 
   const intptr_t shared_table_offset =
-      target::Isolate::class_table_offset() +
-      target::ClassTable::shared_class_table_offset();
+      target::Isolate::shared_class_table_offset();
   const intptr_t table_offset =
       target::SharedClassTable::class_heap_stats_table_offset();
   const intptr_t class_offset = target::ClassTable::ClassOffsetFor(cid);
@@ -2638,8 +2637,7 @@ void Assembler::LoadClassId(Register result, Register object) {
 void Assembler::LoadClassById(Register result, Register class_id) {
   ASSERT(result != class_id);
 
-  const intptr_t table_offset = target::Isolate::class_table_offset() +
-                                target::ClassTable::table_offset();
+  const intptr_t table_offset = target::Isolate::class_table_table_offset();
   LoadIsolate(result);
   movl(result, Address(result, table_offset));
   movl(result, Address(result, class_id, TIMES_4, 0));

assembler_x64.cc

@@ -1864,8 +1864,7 @@ void Assembler::MaybeTraceAllocation(intptr_t cid,
                                      bool near_jump) {
   ASSERT(cid > 0);
   const intptr_t shared_table_offset =
-      target::Isolate::class_table_offset() +
-      target::ClassTable::shared_class_table_offset();
+      target::Isolate::shared_class_table_offset();
   const intptr_t table_offset =
       target::SharedClassTable::class_heap_stats_table_offset();
   const intptr_t class_offset = target::ClassTable::ClassOffsetFor(cid);
@@ -2128,8 +2127,7 @@ void Assembler::LoadClassId(Register result, Register object) {
 
 void Assembler::LoadClassById(Register result, Register class_id) {
   ASSERT(result != class_id);
-  const intptr_t table_offset = target::Isolate::class_table_offset() +
-                                target::ClassTable::table_offset();
+  const intptr_t table_offset = target::Isolate::class_table_table_offset();
 
   LoadIsolate(result);
   movq(result, Address(result, table_offset));