Support latest PXT with GC (#1798)

* Enable gc and basic compilation fixes

* Add missing GC stuff

* Set microbit-dal version

* Disable jacdac in servo

* UTF fixes

* TS build fixes

* Auto-generated files update

* We only seem to have that much

* Fix for new new compiler

* Account for uninitialized scheduler

* Intialize memory allocator

* bump references

* updated package

* Set image tag, requires https://github.com/Microsoft/pxt/pull/5262

* updated project summaries

* Fixing block tests

docs/projects/turtle-spiral.md

@@ -19,11 +19,11 @@ let index = 0
 turtle.setPosition(0, 0)
 turtle.turnRight()
 basic.forever(() => {
-    for (let index = 0; index <= 4; index++) {
+    for (index = 0; index <= 4; index++) {
         turtle.forward(4 - index)
         turtle.turnRight()
     }
-    for (let index = 0; index <= 4; index++) {
+    for (index = 0; index <= 4; index++) {
         turtle.turnLeft()
         turtle.back(index)
     }