Revert shader support for unquantized vertex tables

[DStradley]

The PR for Support unquantized vertex tables #3288 caused GPU slowdowns on performance testing, particularly on slower GPUs. After a lot of investigation and optimizing GPU code, it was found that even after optimization, there was still enough difference to justify splitting the unquantized support into separate shaders, which will be done in a separate PR.

This PR removes support for unquantized vertex tables from the current shaders, and turns off the flag to use unquantized. It does keep an optimized version of shader code for pre-loading the vertex tables, that was also introduced in 3288.

Also learned during this investigation:

• Indexing a vector (rather than accessing its components, at least in cases where it can't be directly replaced by the component version) causes a performance hit and causes zingers on at least some Intel Integrated graphics. An example of this is declaring a "vec4 v", then using it inside a loop like "v[i] = func ();" where i is expected to address x, y, z, w components of the vector sequentially.
• Using a global array (which at assembly level uses an indexable temp register instead of a regular temp register) is a performance hit over separately declared vars. E.g.: using "vec4 g_temp0; vec4 g_temp1; vec4 g_temp2" is better than using "vec4 g_temp[3];"

[pmconne]

@DStradley I am looking into the decoration issue.

[pmconne]

3 failing tests. UPDATE: They're all passing now.

  1) GraphicBuilder
       createMesh
         should preserve polyface normals:

      AssertionError: expected 3 to equal 5
      + expected - actual

      -3
      +5

      at verifyParams (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:170:53)
      at System.IModelApp_1.IModelApp.renderSystem.createMesh (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:157:11)
      at System.createTriMesh (d:\js\s\imodeljs\core\frontend\src\render\RenderSystem.ts:362:17)
      at Mesh.getGraphics (d:\js\s\imodeljs\core\frontend\src\render\primitives\mesh\MeshPrimitives.ts:301:21)
      at GeometryAccumulator.saveToGraphicList (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryAccumulator.ts:207:28)
      at PrimitiveBuilder.finishGraphic (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryListBuilder.ts:168:22)
      at PrimitiveBuilder.finish (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryListBuilder.ts:47:26)
      at test (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:198:30)
      at Context.call (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:203:7)
      at callFn (@/lib/runnable.js:366:21)

  2) GraphicBuilder
       createMesh
         should generate normals for shapes if requested:

      AssertionError: expected 3 to equal 5
      + expected - actual

      -3
      +5

      at verifyParams (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:170:53)
      at System.IModelApp_1.IModelApp.renderSystem.createMesh (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:157:11)
      at System.createTriMesh (d:\js\s\imodeljs\core\frontend\src\render\RenderSystem.ts:362:17)
      at Mesh.getGraphics (d:\js\s\imodeljs\core\frontend\src\render\primitives\mesh\MeshPrimitives.ts:301:21)
      at GeometryAccumulator.saveToGraphicList (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryAccumulator.ts:207:28)
      at PrimitiveBuilder.finishGraphic (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryListBuilder.ts:168:22)
      at PrimitiveBuilder.finish (d:\js\s\imodeljs\core\frontend\src\render\primitives\geometry\GeometryListBuilder.ts:47:26)
      at test (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:216:28)
      at Context.call (d:\js\s\imodeljs\core\frontend\src\test\render\GraphicBuilder.test.ts:221:7)
      at callFn (@/lib/runnable.js:366:21)

  3) VertexLUT
       should produce correct VertexLUT.Params from unquantized MeshArgs:

      AssertionError: expected +0 to equal 128
      + expected - actual

      -0
      +128

      at expectMeshParams (d:\js\s\imodeljs\core\frontend\src\test\render\primitives\VertexTable.test.ts:20:36)
      at Context.call (d:\js\s\imodeljs\core\frontend\src\test\render\primitives\VertexTable.test.ts:185:5)
      at callFn (@/lib/runnable.js:366:21)
      at Test.run (@/lib/runnable.js:354:5)
      at Runner.runTest (@/lib/runner.js:677:10)
      at fn (@/lib/runner.js:801:12)
      at next (@/lib/runner.js:594:14)
      at fn (@/lib/runner.js:604:7)
      at next (@/lib/runner.js:486:14)
      at http://localhost:3000/@/lib/runner.js:572:5