v1.29.0

The key highlights of this release are the change of `pl_gpu` API
semantics to use explicit erroring instead of implicit undefined
behavior, and several important bug fixes related to swapchain resizing
(in particular, handling of suboptimal swapchains); as well as other
minor utility changes, bug fixes and performance improvements.

The new `pl_gpu` API allows clients to duplicate less code related to
checking parameters and capabilities, as long as they're fine with the
resulting error messages they might receive. In particular, libplacebo
no longer aborts on invalid parameters - which helped during initial
development, but is now suffocating clients more than it's helping.

Additions:
- add a new field `pl_fmt.internal_size`, which can differ from
  `texel_size` for emulated formats
- add 16f / 64f texture formats with host-emulated 32f representation
- expose a `pl_vulkan_choose_device` helper function
- add a mechanism for allowing the user to explicitly resize suboptimal
  swapchains rather than having libplacebo take care of it

Changes:
- make `pl_gpu` log and error gracefully on `illegal` parameters rather
  than doing undefined behavior (i.e. aborting)
- creating a `host_mapped` buffer now requires PL_GPU_CAP_MAPPED_BUFFERS
- drop `priv` fields from public structs

Fixes and performance improvements:
- make libplacebo slightly less log spammy in general
- skip the creation/use of semaphores for single-queue usage
- fix several bugs related to swapchain recreation and image acquisition
- fix creation of non-renderable but storable vulkan textures
- fix several bugs related to emulated texture downloads
- fix `pl_fmt` capabilities for some emulated formats
- fix stride/alignment of std430 vectors/matrices
- use push constants more aggressively, whenever possible
- slightly improve accurate of BT.2100 matrices
- fix overzealous rotation of vulkan queues
- fix dangling validation layer suppression in rare cases
- fix possible swapchain deadlock on VK_SUBOPTIMAL_KHR
- handle VK_SUBOPTIMAL_KHR more gracefully / efficiently
This tag has no release notes.