[K/N] Add custom allocator prototype ^KT-55364

Enable custom allocator with -Xallocator=custom.

If the gc is cms (default):
 * a patched version of the memory manager is used that does not build a
   list of allocated objects.
 * a patched version of the cms is used that defers to the allocator for
   sweeping.

Otherwise, a warning is printed, and the allocator is used using the
standard api.

Design doc:
https://docs.google.com/document/d/15xMp-nE-DWL8OrtOc8DoXB80AHUphFICEGjj5K0aNFc

Co-authored-by: Troels Lund <troels@google.com>

Merge-request: KOTLIN-MR-546
Merged-by: Alexander Shabalin <alexander.shabalin@jetbrains.com>

kotlin-native/backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2Native.kt

@@ -324,8 +324,9 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
                     null -> null
                     "std" -> AllocationMode.STD
                     "mimalloc" -> AllocationMode.MIMALLOC
+                    "custom" -> AllocationMode.CUSTOM
                     else -> {
-                        configuration.report(ERROR, "Expected 'std' or 'mimalloc' for allocator")
+                        configuration.report(ERROR, "Expected 'std', 'mimalloc', or 'custom' for allocator")
                         AllocationMode.STD
                     }
                 })