Missing VUIDs for some portability validation requirements

VUIDs appear to be missing for these validation checks in section `23.1. Tessellator` of the spec:

- If vkPhysicalDevicePortabilitySubsetFeaturesKHR::tessellationIsolines is VK_FALSE, then isoline tessellation is not supported by the implementation, and IsoLines must not be used in either tessellation shader stage.
- If VkPhysicalDevicePortabilitySubsetFeaturesKHR::tessellationPointMode is VK_FALSE, then point mode tessellation is not supported by the implementation, and PointMode must not be used in either tessellation shader stage
- GLSL.std.450 fragment interpolation functions are not supported by the implementation and OpCapability must not be set to InterpolationFunction if VkPhysicalDevicePortabilitySubsetFeaturesKHR::shaderSampleRateInterpolationFunctions is VK_FALSE
- If tessellationShader is enabled, and the VK_KHR_portability_subset extension is enabled, and VkPhysicalDevicePortabilitySubsetFeaturesKHR::tessellationIsolines is VK_FALSE, then OpExecutionMode must not be set to IsoLines.

Start with section 23.1, “Tessellator,” and compare the four listed portability validation requirements with the surrounding requirements and their VUIDs. The work is complete when each applicable check has an assigned VUID in the specification and the wording remains consistent with the existing requirements.

Written by the indexing model from the issue text.