Component decoration support

Is it hard to implement I/O component decoration emulation for glsl that don't support it.

```
layout(location = 0, component = 0) in vec2 uv1;
layout(location = 0, component = 2) in vec2 uv2;
```

->

```
in vec4 stage_input_location_0;

// uv1 = stage_input_location_0.xy
// uv2 = stage_input_location_0.zw
```

No files or tests are named. Start from the GLSL examples in the issue and trace how SPIR-V component decorations are translated for GLSL inputs. Done means inputs at location 0 with components 0 and 2 are emulated through one vec4 stage input, with the corresponding component values exposed as shown.

Written by the indexing model from the issue text.