Add an optional handler for detecting memory.grow() use in the runtime

This handler can be used with an import for users not using ESM bindings
to recreate views into memory only when necessary.

Author: CountBleck

Diff for: std/assembly/rt/index.d.ts

@@ -29,6 +29,9 @@ declare function __finalize(ptr: usize): void;
 declare const ASC_RTRACE: bool;
 declare const ASC_PROFILE: bool;
 
+// Memory growth handling
+declare function ASC_RT_GROW_HANDLER(): void;
+
 // Incremental GC constants
 declare const ASC_GC_GRANULARITY: i32;
 declare const ASC_GC_SWEEPFACTOR: i32;

Diff for: std/assembly/rt/stub.ts

@@ -18,6 +18,7 @@ function maybeGrowMemory(newOffset: usize): void {
     if (memory.grow(pagesWanted) < 0) {
       if (memory.grow(pagesNeeded) < 0) unreachable(); // out of memory
     }
+    if (isDefined(ASC_RT_GROW_HANDLER)) ASC_RT_GROW_HANDLER();
   }
   offset = newOffset;
 }

Diff for: std/assembly/rt/tlsf.ts

@@ -444,6 +444,7 @@ function growMemory(root: Root, size: usize): void {
   if (memory.grow(pagesWanted) < 0) {
     if (memory.grow(pagesNeeded) < 0) unreachable();
   }
+  if (isDefined(ASC_RT_GROW_HANDLER)) ASC_RT_GROW_HANDLER();
   let pagesAfter = memory.size();
   addMemory(root, <usize>pagesBefore << 16, <u64>pagesAfter << 16);
 }
@@ -468,7 +469,10 @@ function initialize(): void {
   let rootOffset = (__heap_base + AL_MASK) & ~AL_MASK;
   let pagesBefore = memory.size();
   let pagesNeeded = <i32>((((rootOffset + ROOT_SIZE) + 0xffff) & ~0xffff) >>> 16);
-  if (pagesNeeded > pagesBefore && memory.grow(pagesNeeded - pagesBefore) < 0) unreachable();
+  if (pagesNeeded > pagesBefore) {
+    if (memory.grow(pagesNeeded - pagesBefore) < 0) unreachable();
+    if (isDefined(ASC_RT_GROW_HANDLER)) ASC_RT_GROW_HANDLER();
+  }
   let root = changetype<Root>(rootOffset);
   root.flMap = 0;
   SETTAIL(root, changetype<Block>(0));