add shader for LWRP

[EricWehrly]

Adds a shader that should work with Unity's new Lightweight Render Pipeline.
Had to convert from surface to fragment, but added the lighting and shadow calculations that would otherwise be done for a surface shader.
Should pick up existing material settings used by the tutorial's terrain shader.

[sumosimon]

I cannot compile this script (on URP), my shader coding skills are unfortunately not good enough to provide any insight into why, it may be on my side..
The errors I get are:

(Line 47:)
output TEXCOORD1 used more than once
Compiling Vertex program with DIRECTIONAL FOG_EXP2
Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_RGBM_ENCODING
Disabled keywords: FOG_LINEAR FOG_EXP LIGHTPROBE_SH SHADOWS_SHADOWMASK SHADOWS_SCREEN LIGHTMAP_SHADOW_MIXING UNITY_NO_DXT5nm UNITY_ENABLE_NATIVE_SHADOW_LOOKUPS UNITY_METAL_SHADOWS_USE_POINT_FILTERING UNITY_NO_SCREENSPACE_SHADOWS UNITY_PBS_USE_BRDF2 UNITY_PBS_USE_BRDF3 UNITY_NO_FULL_STANDARD_SHADER UNITY_HARDWARE_TIER1 UNITY_HARDWARE_TIER2 UNITY_HARDWARE_TIER3 UNITY_HALF_PRECISION_FRAGMENT_SHADER_REGISTERS UNITY_LIGHTMAP_DLDR_ENCODING UNITY_LIGHTMAP_FULL_HDR UNITY_VIRTUAL_TEXTURING

(Line 50)
Duplicated input semantics can't change type, size, or layout ('TEXCOORD1').
Compiling Fragment program with DIRECTIONAL FOG_EXP2
Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_RGBM_ENCODING
Disabled keywords: FOG_LINEAR FOG_EXP LIGHTPROBE_SH SHADOWS_SHADOWMASK SHADOWS_SCREEN LIGHTMAP_SHADOW_MIXING UNITY_NO_DXT5nm UNITY_ENABLE_NATIVE_SHADOW_LOOKUPS UNITY_METAL_SHADOWS_USE_POINT_FILTERING UNITY_NO_SCREENSPACE_SHADOWS UNITY_PBS_USE_BRDF2 UNITY_PBS_USE_BRDF3 UNITY_NO_FULL_STANDARD_SHADER UNITY_HARDWARE_TIER1 UNITY_HARDWARE_TIER2 UNITY_HARDWARE_TIER3 UNITY_HALF_PRECISION_FRAGMENT_SHADER_REGISTERS UNITY_LIGHTMAP_DLDR_ENCODING UNITY_LIGHTMAP_FULL_HDR UNITY_VIRTUAL_TEXTURING

(Line 116) [this goes away if i.fogCoord is changed to IN.fogCoord]
invalid subscript 'fogCoord'
Compiling Vertex program with DIRECTIONAL FOG_EXP2
Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_RGBM_ENCODING
Disabled keywords: FOG_LINEAR FOG_EXP LIGHTPROBE_SH SHADOWS_SHADOWMASK SHADOWS_SCREEN LIGHTMAP_SHADOW_MIXING UNITY_NO_DXT5nm UNITY_ENABLE_NATIVE_SHADOW_LOOKUPS UNITY_METAL_SHADOWS_USE_POINT_FILTERING UNITY_NO_SCREENSPACE_SHADOWS UNITY_PBS_USE_BRDF2 UNITY_PBS_USE_BRDF3 UNITY_NO_FULL_STANDARD_SHADER UNITY_HARDWARE_TIER1 UNITY_HARDWARE_TIER2 UNITY_HARDWARE_TIER3 UNITY_HALF_PRECISION_FRAGMENT_SHADER_REGISTERS UNITY_LIGHTMAP_DLDR_ENCODING UNITY_LIGHTMAP_FULL_HDR UNITY_VIRTUAL_TEXTURING

(Line 47)
Duplicate non-system value semantic definition: output semantic 'TEXCOORD1' and output semantic 'TEXCOORD1'
Compiling Vertex program with DIRECTIONAL FOG_EXP2
Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_RGBM_ENCODING
Disabled keywords: FOG_LINEAR FOG_EXP LIGHTPROBE_SH SHADOWS_SHADOWMASK SHADOWS_SCREEN LIGHTMAP_SHADOW_MIXING UNITY_NO_DXT5nm UNITY_ENABLE_NATIVE_SHADOW_LOOKUPS UNITY_METAL_SHADOWS_USE_POINT_FILTERING UNITY_NO_SCREENSPACE_SHADOWS UNITY_PBS_USE_BRDF2 UNITY_PBS_USE_BRDF3 UNITY_NO_FULL_STANDARD_SHADER UNITY_HARDWARE_TIER1 UNITY_HARDWARE_TIER2 UNITY_HARDWARE_TIER3 UNITY_HALF_PRECISION_FRAGMENT_SHADER_REGISTERS UNITY_LIGHTMAP_DLDR_ENCODING UNITY_LIGHTMAP_FULL_HDR UNITY_VIRTUAL_TEXTURING

(Line 50)
Duplicate non-system value semantic definition: output semantic 'TEXCOORD1' and output semantic 'TEXCOORD1'
Compiling Vertex program with DIRECTIONAL FOG_EXP2
Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_RGBM_ENCODING
Disabled keywords: FOG_LINEAR FOG_EXP LIGHTPROBE_SH SHADOWS_SHADOWMASK SHADOWS_SCREEN LIGHTMAP_SHADOW_MIXING UNITY_NO_DXT5nm UNITY_ENABLE_NATIVE_SHADOW_LOOKUPS UNITY_METAL_SHADOWS_USE_POINT_FILTERING UNITY_NO_SCREENSPACE_SHADOWS UNITY_PBS_USE_BRDF2 UNITY_PBS_USE_BRDF3 UNITY_NO_FULL_STANDARD_SHADER UNITY_HARDWARE_TIER1 UNITY_HARDWARE_TIER2 UNITY_HARDWARE_TIER3 UNITY_HALF_PRECISION_FRAGMENT_SHADER_REGISTERS UNITY_LIGHTMAP_DLDR_ENCODING UNITY_LIGHTMAP_FULL_HDR UNITY_VIRTUAL_TEXTURING