tex-miplevel-selection: test all variants of textureLod
all.py: mark old tex-miplevel-selection tests as concurrent
tex-level-selection: deduplicate code, improve output
tex-miplevel-selection: test all variants of texture() with bias
tex-miplevel-selection: test all variants of textureOffset
tex-miplevel-selection: test all variants of textureOffset with bias

+ some bug fixes
tex-miplevel-selection: test all variants of textureProj
tex-miplevel-selection: test all variants of textureProj with bias
tex-miplevel-selection: test all variants of textureProjOffset
tex-miplevel-selection: simplify shader code generation
tex-miplevel-selection: test all variants of textureProjOffset with bias

+ a comment about offsets
tex-miplevel-selection: test all variants of textureLodOffset
tex-miplevel-selection: test all variants of textureProjLod
tex-miplevel-selection: test all variants of textureProjLodOffset

+ Use level 0 texture coordinates to really verify the Lod fetch works.
  It was using scaled coordinates, so textureLodOffset could have been
  replaced by textureOffset and the test would pass. Now the test will
  fail if drivers attempt to fake it that way.
tex-miplevel-selection: test all variants of textureGrad
tex-miplevel-selection: test all variants of textureGradOffset
tex-miplevel-selection: test all variants of textureProjGrad
tex-miplevel-selection: test all variants of textureProjGradOffset
tex-miplevel-selection: test all texture functions with Rect targets

+ off-by-one error fix in check_result
tex-miplevel-selection: fix cubemap targets for texture() and texture(bias)