Rollup merge of #82421 - sunfishcode:wasi-metadata-size, r=alexcrichton
Rollup merge of #82421 - sunfishcode:wasi-metadata-size, r=alexcrichton

Add a `size()` function to WASI's `MetadataExt`.

WASI's `filestat` type includes a size field, so expose it in
`MetadataExt` via a `size()` function, similar to the corresponding Unix
function.

r? ``````@alexcrichton``````

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust