Make bun.webcore.Blob smaller and ref-counted (#23015)

Reduce the size of `bun.webcore.Blob` from 120 bytes to 96. Also make it
ref-counted: in-progress work on improving the bindings generator
depends on this, as it means C++ can pass a pointer to the `Blob` to Zig
without risking it being destroyed if the GC collects the associated
`JSBlob`.

Note that this PR depends on #23013.

(For internal tracking: fixes STAB-1289, STAB-1290)

src/StandaloneModuleGraph.zig

@@ -199,7 +199,6 @@ pub const StandaloneModuleGraph = struct {
                 store.ref();
 
                 const b = bun.webcore.Blob.initWithStore(store, globalObject).new();
-                b.allocator = bun.default_allocator;
 
                 if (bun.http.MimeType.byExtensionNoDefault(bun.strings.trimLeadingChar(std.fs.path.extension(this.name), '.'))) |mime| {
                     store.mime_type = mime;