This major release brings with it a number of fixes and changes for
compatibility with both upstream and downstream projects, native HDR
output on D3D11, and a complete redesign of the way ICC profiles are

- add helper macros linearize() and delinearize(), expanding to the
  definition of the gamma function in use for the video signal
- add various new helper functions relating to colorspaces and
  primaries, see the API change log for a more comprehensive list
- add `pl_render_params.force_low_bit_depth_fbos` for
  debugging/performance tweaking purposes
- add `pl_plane.flipped`, to allow representing individual flipped
  frames in a way that semantically decouples from the presentation rect
  (e.g. for OpenGL framebuffers, or planes with negative stride)
- add '%' and '=' as operators to custom shaders, matching mpv
- add `pl_vulkan.(un)lock_queue` for interop with other libraries
- add `pl_frame.acquire/release` for better interop with hardware
  decoders. These are only called on an as-needed basis immediately
  before and after a frame is actually used for rendering, with only one
  frame being acquired at any given time
- add `pl_film_grain_from_av` helper function
- add support for configuring the swapchain color space on D3D11, using
  the existing pl_swapchain_colorspace_hint mechanism
- add an entirely new ICC profile shader API, allowing ICC profiles to
  be persistently opened (pl_icc_open) and their metadata exposed,
  with explicit `pl_icc_decode` and `pl_icc_encode` operations instead
  of a single monolithic decode+apply step
- add `pl_render_params.plane_up/downscaler`, allowing to override the
  upscaler/downscaler for subsampled chroma planes in particular
- ad `pl_filter_function/config.name` for debugging/logging purposes

- pl_log_create is no longer an exported symbol, instead becoming
  versioned by the compiled API version. `pl_log_create` is now a macro
  expanding to the name of this versioned function
- `pl_overlay_part` has been refactored, adding the new field `coords`
  to control the coordinate system relative to which the part is placed
  on-screen, as well as being generalized to support floating point
- deprecate PL_HOOK_PRE_OVERLAY, as a result of overlays no longer being
  applied during the rendering pipeline
- default `pl_color_map_params.gamut_mode` to PL_GAMUT_CLIP, replacing
- DRM modifiers are now required for vulkan dmabuf interop
- `pl_vulkan.queue_*` are now *always* set to valid queues for that
  operation type, even if it means including duplicates
- `pl_render_image` with NULL image now reports itself as a blend pass
  (blending 0 frames) instead of a frame pass to the info callbacks
- completely refactor/remove the old ICC/3DLUT shader API
  (`pl_icc_update`, `pl_icc_apply` etc.)
- <libplacebo/shaders/icc.h> is now installed unconditionally, with
  `pl_icc_open` simply failing when built without lcms2

Fixes and performance enhancements:
- fix pl_tone_map_reinhard.param_min to prevent division by zero
- fix left-over asserts preventing misaligned buffer uploads via
- fix bug where emulated rgb textures had alpha incorrectly
  preinitialized to 0 instead of 1
- overlays are now always rendered onto the final blended image, solving
  various bugs and unexpected edge cases due to image overlays being
  blended in the middle of the rendering pipeline
- fix a bug where tone-mapping without a state object resulted in broken
- allow `pl_shader_sample_polar` to work with external samplers or
  flipped textures without incurring a performance penalty
- fix the behavior of pl_shader_sample_oversample, which was previously
  producing very wrong results
- fix an issue where the dither depth was incorrectly picked in a number
  of edge cases
- fix a number of issues with the H.274 film grain shader
- fix a bug where grayscale images were slightly too green
- fix a bug where `pl_vulkan.queue_transfer` was never set
- fix possible UB in pl_opengl_wrap_tex on some drivers with broken
  texture channel depth queries
- fix issue where some shader LUTs were being regenerated on every
  single frame rather than properly cached
- fix shader compilation error on older GLSL
- fix bug where images were sometimes undesiredly being scaled in linear
- fix SDR<->SDR tone-mapping to properly be a no-op (linear stretch)
- fix use-after-free in pl_get_buffer2's error path
- fix d3d11 build issues on older versions of the SDK
- fix edge case where auto-detected vulkan in the absence of
  glslang/shaderc caused the build to fail
- fix build issues with up-to-date vulkan SDK
- fix issue where non-coherent buffer imports were used in ways not
  adhering to the non-coherent memory atom size
- fix various issues and undefined behavior when flushing mapped
  buffers, especially for non-coherent memory
- avoid some validation warnings about improper pipeline barriers
- fix runtime error with up-to-date MoltenVK
- fix issue where some pl_frame_mix structs resulted no frames being
  mixed, triggering an assertion
- fix bug where overlays were drawn flipped onto flipped planes when
  rendering a NULL image