URP Simple Lit shader does not bind lightmaps correctly

Steps to reproduce:

1. Download [Internal link] project (pull LightBaker branch)
2. Open Market-Nighttime scene
3. Make sure that Double Sided Global Illumination is unchecked in the material properties
4. Make sure that Auto Generate and Progressive Updates are unchecked
5. Bake lighting using CPULM or GPULM

Expected result:

• Lightmaps are correctly applied to world geometry

Actual result:

• Lightmaps are lacking indirect bounce, and are incorrectly composited. Errors are thrown in the console (see [Internal link])

Notes:

• The following error is thrown in the console: Metal: Fragment shader missing texture binding at index 0 (unity_Lightmap / Universal Render Pipeline/Simple Lit)
• When baking with the GPULM, the following errors are thrown: 
  [BakePipeline::BakeStage] Bake took 17030.24ms and failed with code 5.

 #0 GetStacktrace(int)
 #1 DebugStringToFile(DebugStringToFileData const&)
 #2 (anonymous namespace)::RunBake(void*)
 #3 Thread::RunThreadWrapper(void*)
 #4 _pthread_start
 #5 thread_start

• Clearing baked data, library folder, GI or shader cache does not fix the issue
• Observed in 582a02a42f59