This is a major reworking of the way the debugger is implemented. Instead of generating shader code that is continually driving `vk::dbg` state, the debugger now: * Maintains a full shadow copy of all Intermediate values (SSA) * Only calls out to C++ whenever a trap is set * Only constructs and updates the `vk::dbg` state when a trap is hit The main goal of this reworking is to properly support OpenCL.Debug.100's DebugValue instructions that may use deref expressions (See https://www.khronos.org/registry/spir-v/specs/unified1/OpenCL.DebugInfo.100.html#_debug_operations_a_id_operation_a) These are remarkably hard to implement without having everything backed with real memory. The resulting reimplementation is: * Much, much faster (>1000x faster for sample apps I've tried). Only ~2x slower than non-debug enabled SwiftShader now. * Uses much less runtime memory. * Much cleaner, removing a load of template magic for setting variable state that was extremely hard to follow * More thoroughly commented, explaining each component and method. Bug: b/145351270 Change-Id: I1b48e9defae095109ebfaf90dfb7c7e22d335816 Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48729Reviewed-by: Nicolas Capens <nicolascapens@google.com> Reviewed-by: Antonio Maiorano <amaiorano@google.com> Kokoro-Result: kokoro <noreply+kokoro@google.com> Tested-by: Ben Clayton <bclayton@google.com>