gpu: Added helpers to BindGroup.Entry; make dynamic_offset a const slice (#215)

Helps hexops/mach#

gpu/src/BindGroup.zig

@@ -35,6 +35,34 @@ pub const Entry = struct {
     size: u64,
     sampler: ?Sampler = null,
     texture_view: ?TextureView = null,
+
+    /// Helper to create a buffer BindGroup.Entry.
+    pub fn buffer(binding: u32, buf: Buffer, offset: u64, size: u64) Entry {
+        return .{
+            .binding = binding,
+            .buffer = buf,
+            .offset = offset,
+            .size = size,
+        };
+    }
+
+    /// Helper to create a sampler BindGroup.Entry.
+    pub fn sampler(binding: u32, sam: Sampler) Entry {
+        return .{
+            .binding = binding,
+            .sampler = sam,
+            .size = 0,
+        };
+    }
+
+    /// Helper to create a texture view BindGroup.Entry.
+    pub fn textureView(binding: u32, texview: TextureView) Entry {
+        return .{
+            .binding = binding,
+            .texture_view = texview,
+            .size = 0,
+        };
+    }
 };
 
 pub const Descriptor = struct {