fix(fs): reject negative offsets when seeking from the start (#3633)

In plugins/fs/src/commands.rs seek, `SeekFrom::Start(offset as u64)`
turned -1 into u64::MAX. The offset is now converted with u64::try_from
and a negative one is an error. E2E spec added.

.changes/fix-fs-seek-negative.md

@@ -0,0 +1,6 @@
+---
+fs: patch
+fs-js: patch
+---
+
+`FileHandle.seek` now rejects a negative offset with `SeekMode.Start` instead of seeking to a huge position.