molten-vk: install ICD to non-overridable path

[cho-m]

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For #203233. May as well use non-overridable path to reduce chances of user configuration impacting functionality.

Prior bottle,

❯ XDG_DATA_DIRS=/tmp vulkaninfo --summary
ERROR: [Loader Message] Code 0 : vkCreateInstance: Found no drivers!
Cannot create Vulkan instance.
This problem is often caused by a faulty installation of the Vulkan driver or attempting to use a GPU that does not support Vulkan.
ERROR at /tmp/vulkan-tools-20241221-15121-nec5zd/Vulkan-Tools-1.4.304/vulkaninfo/./vulkaninfo.h:456:vkCreateInstance failed with ERROR_INCOMPATIBLE_DRIVER

❯ vulkaninfo --summary | rg driver
VK_LUNARG_direct_driver_loading        : extension revision 1
	driverVersion      = 0.2.2019
	driverID           = DRIVER_ID_MOLTENVK
	driverName         = MoltenVK
	driverInfo         = 1.2.11
	driverUUID         = 4d564b00-0000-27e3-0f02-020700000000

New build:

❯ XDG_DATA_DIRS=/tmp vulkaninfo --summary | rg driver
VK_LUNARG_direct_driver_loading        : extension revision 1
	driverVersion      = 0.2.2019
	driverID           = DRIVER_ID_MOLTENVK
	driverName         = MoltenVK
	driverInfo         = 1.2.11
	driverUUID         = 4d564b00-0000-27e3-0f02-020700000000

[cho-m]

We could keep a relative path if preferred. Absolute path is simpler for inreplace. Relative path does avoid relocation in JSON file (though wouldn't expect performance impact unlike relocation in binary file).

Suggested change

	"\"./libMoltenVK.dylib\"",
	"\"#{lib}/libMoltenVK.dylib\""
	"./libMoltenVK.dylib",
	(lib/"libMoltenVK.dylib").relative_path_from(prefix/"etc/vulkan/icd.d")