Fix visualization tests

[RaananW]

Two issues I found with newly added tests:

glTF Clear Coat:

In config.json gl are lower case. this works in windows, but fails on linux (which is the reason webgl1 and webgpu tests fail).

Render To 3D RT - snapshot was missing.

If you wonder why it worked in WebGL2 - the WebGL2 tests were set to run twice in case the first time fails. When playwright doesn't find a snapshot it generates it. So - WebGL2 failed the first time because of missing snapshots, and then generated it and re-ran the tests.

This was corrected!

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

Snapshot stored with reference name:
refs/pull/14956/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14956/merge/index.html

To test a playground add it to the URL, for example:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14956/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/14956/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/14956/merge
https://gui.babylonjs.com/?snapshot=refs/pull/14956/merge
https://nme.babylonjs.com/?snapshot=refs/pull/14956/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/14956/merge#BCU1XR#0

[bjsplat]

WebGL2 visualization test reporter:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14956/merge/testResults/webgl2playwright/index.html

[bjsplat]

Visualization tests for WebGPU (Experimental)
Important - these might fail sporadically. This is an optional test.

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14956/merge/testResults/webgpuplaywright/index.html