nir/algebraic: Add missing 16-bit extract_[iu]8 patterns

No shader-db changes on any Intel platform.

v2: Use a loop to generate patterns.  Suggested by Jason.

v3: Fix a copy-and-paste bug in the extract_[ui] of ishl loop that would
replace an extract_i8 with and extract_u8.  This broke ~180 tests.  This
bug was introduced in v2.

Reviewed-by: Matt Turner <mattst88@gmail.com> [v1]
Reviewed-by: Dylan Baker <dylan@pnwbakers.com> [v2]
Acked-by: Jason Ekstrand <jason@jlekstrand.net> [v2]
21 jobs for !369 with review/intel-extract-fixes in 22 minutes and 37 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #163241
ubuntu

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  Build+Test
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make-gallium-drivers-other

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make-gallium-drivers-radeonsi

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make-gallium-drivers-swr

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make-gallium-st-clover-llvm

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make-gallium-st-clover-llvm-39

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make-gallium-st-other

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make-loader-classic-dri

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make-vulkan

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meson-gallium-clover-llvm

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meson-gallium-clover-llvm39

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meson-gallium-drivers-other

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meson-gallium-radeonsi

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meson-gallium-st-other

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meson-gallium-swr

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meson-glvnd

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meson-loader-classic-dri

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meson-vulkan

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scons-llvm

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scons-nollvm

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scons-swr

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