Change `windowSpacePosition` from c-array to `std::array`. Other invocation state fields use `std::array`, and this simplifies some template logic in the new debugger implementation.

Add / fix comments in `SpirvShaderControlFlow.cpp`.
Also add a missing call to `dbgEndEmitInstruction()`. This is typically invoked by `SpirvShader::EmitInstruction()`, but the special handling of `OpPhi` in `EmitLoop()` previously skipped this.

Bug: b/145351270
Change-Id: Id6463d5e157b28ef61ce8fc48644bcbc97a2aa55
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48696Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>