Immersive mode: fix gamma, raise quad resolution, stop duplicate compositing (#1846)

* Skip hidden-surface compositing while the immersive session owns presentation

The native render loop parks on its condvar and only renders when a content
update dirties it. With the XR bridge attached, the quad samples the
AHardwareBuffer directly, so forwarding the frame and returning before
nativeUpdateWindowContentAHB leaves the native Vulkan compositor idle — no
scene draw and no present to the invisible surface, per game frame. Flat mode
is unchanged; the bridge is null there.

* Raise the immersive swapchain to 1920x1080 and fix gamma via an sRGB swapchain

The 720p intermediate was the quality ceiling: game frames were sampled down
into it and back up onto the quad. The prior 1080p attempt measured worse, but
that was against a pipeline still paying the per-frame EGLImage recreate and
the duplicate hidden-surface compositor, both since removed.

Gamma: the swapchain preferred linear GL_RGBA8 while the content is
sRGB-encoded, so the compositor double-applied the transfer (washed-out
output). Prefer GL_SRGB8_ALPHA8 and linearize sampled content in the shaders,
since GLES re-encodes on write to sRGB attachments; a linear-format fallback
keeps old behavior when sRGB is not offered.

libxrimmersive.so rebuilt (NDK 27.3.13750724) for both XR flavors.

* Render the composited scene into a shared AHardwareBuffer for the immersive session

* Let the immersive session run at the system default refresh rate

* Forward ASurfaceRenderer game buffers to the immersive session

* Gate the immersive bridge attach points to XR builds

* Drop the ASR immersive forwarding; keep bridge re-attach on renderer change

* Harden the XR scene target: resize handling, memory-type guard, write-completion fence, real extents

* Follow the container screen size and a per-container refresh rate in immersive mode

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Co-authored-by: Utkarsh Dalal <utkarsh.dalal@toptal.com>