The function ShaderVariable::getNestedArraySize needs to return at least
1 entry for unsized arrays to ensure the shader buffer sizes are
reported correctly.

This also allows ANGLE to treat unsized arrays of structs and basic
types the same way, allowing for the special treatment of unsized arrays
in TraverseStructArrayVariable() to be removed.

Bug: angleproject:3596
Test: dEQP-GLES31.functional.program_interface_query.shader_storage_block.buffer_data_size.*
Change-Id: I3b2a3a68c25e0913b79e989d7c719b34ce9b75fd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1934952
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>