Add a migration guide from 0.15 to 0.16 (#6233)

### What
* Closes #6232

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6233?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6233?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
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usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

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---------

Co-authored-by: Clement Rey <[email protected]>

docs/content/reference/migration.md

@@ -1,5 +1,5 @@
 ---
 title: Migration Guides
 order: 900
-redirect: reference/migration/migration-0-15
+redirect: reference/migration/migration-0-16
 ---

docs/content/reference/migration/migration-0-16.md

@@ -0,0 +1,72 @@
+---
+title: Migrating from 0.15 to 0.16
+order: 160
+---
+
+
+## `timeless` replaced by `static`
+
+The concept of _timeless_ data has been replaced by _static_ data.
+Except for the name change, they behave similarly in most use cases.
+
+Static data is data that shows up at all times, on all timelines.
+
+In 0.15, you could log component data to the same entity path using both timeless and temporal data, and the resulting component data would end up being the concatenation of the two.
+
+0.16 introduces static data, which has a far simpler model: if you log static component data to an entity path, it unconditionally overrides any other data (whether static or temporal) for that component.
+Once static data has been logged, it can only be overwritten by other static data.
+
+Static data is most often used for `AnnotationContext` and `ViewCoordinates`.
+
+
+#### C++
+
+```diff
+- rec.log_timeless("world", rerun::ViewCoordinates::RIGHT_HAND_Z_UP);
++ rec.log_static("world", rerun::ViewCoordinates::RIGHT_HAND_Z_UP);
+```
+
+#### Python
+
+```diff
+- rr.log("world", rr.ViewCoordinates.RIGHT_HAND_Z_UP, timeless=True)
++ rr.log("world", rr.ViewCoordinates.RIGHT_HAND_Z_UP, static=True)
+```
+
+#### Rust
+
+```diff
+- rec.log_timeless("world", &rerun::ViewCoordinates::RIGHT_HAND_Z_UP)?;
++ rec.log_static("world", &rerun::ViewCoordinates::RIGHT_HAND_Z_UP)?;
+```
+
+
+## `MeshProperties` replaced by `TriangleIndices`
+
+In PR [#6169](https://github.com/rerun-io/rerun/pull/6169) we replaced `MeshProperties` with `TriangleIndices`. We could do this thanks to simplifications in our data model.
+
+#### C++
+
+```diff
+  rerun::Mesh3D(positions)
+-     .with_mesh_properties(rerun::components::MeshProperties::from_triangle_indices({{2, 1, 0}}))
++     .with_triangle_indices({{2, 1, 0}})
+```
+
+#### Python
+
+```diff
+  rr.Mesh3D(
+      vertex_positions=…,
+-     indices=[2, 1, 0],
++     triangle_indices=[2, 1, 0],
+  ),
+```
+
+#### Rust
+
+```diff
+  rerun::Mesh3D::new(positions)
+-     .with_mesh_properties(rerun::MeshProperties::from_triangle_indices([[2, 1, 0]]))
++     .with_triangle_indices([[2, 1, 0]])
+```