[TextureMapper] Use linear sampling when blurring for better performance

[Aki-7]

437b554

[TextureMapper] Use linear sampling when blurring for better performance
https://bugs.webkit.org/show_bug.cgi?id=261102

Reviewed by Fujii Hironori.

To reduce the GPU load for gaussian blur, this fix reduces the size of
kernel use for the blur.

By adjusting the position(offset) to sample the texture and the weight
of each element of the kernel so that the linear interpolation during
texture sampling samples two texels and properly weights them, we can
reduce the size of the kernel without changing behaviour.

* Source/WebCore/platform/graphics/texmap/TextureMapperGL.cpp:
(WebCore::kernelHalfSizeToSimplifiedKernelHalfSize):
(WebCore::computeGaussianKernel):
(WebCore::TextureMapperGL::drawBlurred):
* Source/WebCore/platform/graphics/texmap/TextureMapperShaderProgram.cpp:
* Source/WebCore/platform/graphics/texmap/TextureMapperShaderProgram.h:

Canonical link: https://commits.webkit.org/267715@main

76f7aff

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	🛠 watch
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash c25145b)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	❌ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	❌ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	❌ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	❌ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[Aki-7]

This change will confilict with #17469.
I'll remove draft status after merging/closing #17469

[webkit-early-warning-system]

EWS run on current version of this PR (hash 76f7aff)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	🛠 watch
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 267715@main (437b554): https://commits.webkit.org/267715@main

Reviewed commits have been landed. Closing PR #17471 and removing active labels.