Vendor wgpu-hal 29.0.4 and i-slint-renderer-skia 1.17.1, unmodified

The Android develop view reads its frame back through memory (TD-1)
because wgpu's Vulkan swapchain never pre-rotates, and a portrait window
on this tablet's landscape panel then tears. The fix is a small patch to
each of these two crates, and this commit is only the ground it lands on:
both are byte-for-byte the crates.io sources the lockfile already
resolved, so the commits that follow are the patch and nothing else.

third_party/ is excluded from the workspace, or every path dependency
under the root would become a member and `--workspace` would test and
lint upstream code as ours. The README says how to carry the patches
across a Slint or wgpu bump, which matters because a stale version here
does not fail the build — cargo just warns and uses the unpatched crate.

third_party/README.md

@@ -0,0 +1,35 @@
+# Patched upstream crates
+
+Each directory here is a crate exactly as crates.io publishes it, at the
+version `Cargo.lock` resolves, with a local patch on top. The root
+`Cargo.toml` routes the dependency here through `[patch.crates-io]`; the
+directory is excluded from the workspace, so `cargo test --workspace`,
+clippy and fmt leave it alone.
+
+The first commit that adds a directory is the pristine copy (from
+`~/.cargo/registry/src/*/<crate>-<version>`, minus `.cargo-ok` and the
+crate's own `Cargo.lock`). Every later commit touching it is ours, so
+`git log -p -- third_party/<dir>` is the patch and nothing else.
+
+## Carrying a patch forward
+
+When Slint or wgpu is bumped, the version here stops matching and cargo
+warns that the patch is unused — the build then silently goes back to the
+unpatched crate. So a bump is:
+
+1. Copy the new version in beside the old one, as its own commit.
+2. Re-apply the diff from `git log -p` on the old directory.
+3. Point `[patch.crates-io]` at the new directory and delete the old one.
+4. Re-check on the device (below) — both patches are behaviour that only a
+   rotated Android display exercises.
+
+Drop a patch entirely once upstream has the fix; each section says what
+upstream change would make it unnecessary.
+
+## wgpu-hal 29.0.4 — Vulkan pre-rotation on Android
+
+*(patch lands in the next commit)*
+
+## i-slint-renderer-skia 1.17.1 — rotate the canvas to match
+
+*(patch lands in a later commit)*