android: expose RenderableManager.PrimitiveType value

**Description**

Our Android renderer changes the primitive topology of loaded glTF assets at
runtime. Code outside `com.google.android.filament` needs to pass
`PrimitiveType` through JNI to `RenderableManager::setGeometryAt()`.

However, `PrimitiveType.getValue()` is package-private, so it cannot be used by
external Android integrations.

**Requested change**

Make the existing method public:

```java
public int getValue() { return mType; }
```

Proposed change:

https://github.com/eqgis/filament/commit/8eee1d258732723ebc16b746da8127fbe0ea4a5b

This only changes Java API visibility and does not affect rendering behavior.

**Platform**

Android Java/JNI, backend-independent. The change has been validated with
`assembleDebug`.

Locate RenderableManager.PrimitiveType in the Android Java API and inspect the existing getValue() method. Make the method publicly accessible without changing its returned value, then run assembleDebug to verify the Android build succeeds.

Written by the indexing model from the issue text.