Wasm2JS double heap assignments get split into two i32 assignments.

In https://github.com/juj/wasm_webgpu/commit/4c2600b0f6549f95fe9251cba629c935fbc74ba8, I have the following code:

```c
WGpuRenderPassColorAttachment colorAttachment = {};
...
colorAttachment.loadColor[3] = 0.05;
```
here `loadColor` struct member is of type `double loadColor[4]`. When building with WASM2JS, I see

```js
HEAP32[$1 + 88 >> 2] = -1259857073;
HEAP32[$1 + 92 >> 2] = 1063997057;
```
getting generated for the double number heap set operation, instead of a
```js
HEAPF64[$1 + 88 >> 3] = 0.05;
```
I wonder if this is some special case, or if Wasm2JS does not do HEAPF64 assignments?