Shader compile errors carry no message: WEBMIN strips glslang's diagnostics

## Problem

Every failing shader compile reports only:

```
ERROR: 3 compilation errors. No code generated.
```

No file, line, or reason. The failing construct can only be found by bisecting the shader source.

## Cause

`Dependencies/CMakeLists.txt` sets `ENABLE_GLSLANG_WEBMIN ON` (and `ENABLE_GLSLANG_WEBMIN_DEVEL OFF`). `ENABLE_GLSLANG_WEBMIN` defines `GLSLANG_WEB` on the glslang targets (`glslang/CMakeLists.txt:279-283`), and `ParseHelper.h:107` guards the diagnostic emitters on it:

```cpp
#if !defined(GLSLANG_WEB) || defined(GLSLANG_WEB_DEVEL)
virtual void C_DECL error(const TSourceLoc&, const char* szReason, ...);
virtual void C_DECL warn(...);
virtual void C_DECL ppError(...);
virtual void C_DECL ppWarn(...);
#endif
```

The error *count* still increments, so failures are detected — only the text is discarded.

## Impact

Shader authors and anyone debugging the ShaderCompiler get no actionable output. This cost real time while investigating #1818, where the failing constructs were identifiable only by bisection.

Same shape as the `SPIRV_CROSS_WEBMIN` opcode stripping already noted in #1808: a size-optimised dependency silently discarding diagnostics.

## Options

- Turn on `GLSLANG_WEB_DEVEL` — restores the text, costs binary size.
- Restore just the message text in the `BabylonJS/glslang` fork without the rest of the DEVEL surface.
- Enable diagnostics only in `Debug`/`RelWithDebInfo`, keeping `Release` minimal.

Worth deciding against measured size numbers rather than assumption; the same question applies to the spirv-cross fork.

---

[Filed by Copilot on behalf of @bghgary]

Read Dependencies/CMakeLists.txt, glslang/CMakeLists.txt around lines 279-283, and ParseHelper.h around line 107 to confirm how WEBMIN removes diagnostic emitters. Compare the listed options using measured binary-size impact; done means shader failures report actionable file, line, and reason information without an unacceptable size increase.

Written by the indexing model from the issue text.