Implementation of #137341
This adds support for using references to any variable in a local scope
inside the shader codebase.
Example:
```cpp
int a = 0;
int &b = a;
b++; /* a == 1 */
```
Using `auto` is supported for reference definition as the type is not
preserved by the copy paste procedure. Type checking is done by the
C++ shader compilation or after the copy paste procedure during shader
compilation. `auto` is still unsupported for other variable declarations.
Reference to opaque types (`image`, `sampler`) are supported since
they are never really assigned to a temp variable.
This implements all safety feature related to the implementation being
copy pasting the definition string. That is:
- No `--`, `++` operators.
- No function calls.
- Array subscript index needs to be int constants or constant variable.
The copy pasting does not replace member access:
`auto &a = b; a.a = c;` becomes `b.a = c;`
The copy pasting does not replace function calls:
`auto &a = b; a = a();` becomes `b = a();`
While limited, this already allows for nicer syntax (aliasing) for
accessing SSBOs and the potential overhead of a copy semantic:
```cpp
ViewMatrices matrices = drw_view_buf[0];
matrices.viewmat = float4x4(1);
drw_view_buf[0] = matrices;
```
Can now be written as;
```cpp
ViewMatrices &matrices = drw_view_buf[0];
matrices.viewmat = float4x4(1);
```
Which expands to;
```cpp
drw_view_buf[0].viewmat = float4x4(1);
```
Note that the reference semantic is not carried through function call
because arguments are transformed to `inout` in GLSL. `inout` has
copy semantic but it is often implemented as reference by some
implementations.
Another important note is that this copy-pasting doesn't check if a
symbol is a variable. It can match a typename. But given that our
typenames have different capitalizations style this is unlikely to be
an issue. If that issue arise, we can add a check for it.
Rel #137446
Pull Request: https://projects.blender.org/blender/blender/pulls/138412
2513fbedca