WGSL texture_2d_array with 1 layer is not translated to an array texture for WebGL2 GLSL

[superdump]

Description
Using a depth buffer texture_2d_array with 1 layer in WGSL works fine with Vulkan, Metal, etc. But with WebGL2 it is translated as a non-array texture and fails silently.

Repro steps
There is an example in #2138 that exhibits this issue. Please shout at me if you want me to test something!

Expected vs observed behavior
Expected: Array texture shadow map with 1 layer works as it does for native.
Observed: Silent failure.

Platform
Windows 10, wpgu master, WebGL2.

[kvark]

GLES backend guesses the type of the texture currently: it checks for n==1, and it checks for n % 6, both are crappy. There needs to be a proper solution instead of this guesswork, but I don't know what this is yet.

[teoxoy]

Related: #1614

[cwfitzgerald]

Closing in favor of #1614