Reland "Add a per-thread proc table using thread local storage"

This is a reland of b04a92f01b
with the deletion of a duplicate exported function in dawn_wire that
was causing a compilation failure on Windows.

Original change's description:
> Add a per-thread proc table using thread local storage
>
> In situations where both dawn_wire and dawn_native are used on separate
> threads (Chrome with --single-process or --in-process-gpu), it's
> desirable to have a per-thread proc table so that the WebGPU C++ API can
> still be used. This eliminates classes of bugs with manual
> reference/release errors.
>
> This also changes many of the GetProcs functions to return const
> references to the static proc tables known at compile time, instead of a
> copy.
>
> Bug: none
> Change-Id: I8775bb715b312dd9476a1903fbd797d4b1302614
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/29240
> Reviewed-by: Stephen White <senorblanco@chromium.org>
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Commit-Queue: Austin Eng <enga@chromium.org>

Bug: none
Change-Id: Id90e5372132cd93a2f8631c8185d0e71b01bc1af
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/29443
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>

generator/templates/dawn_thread_dispatch_proc.cpp

@@ -0,0 +1,52 @@
+#include "dawn/dawn_thread_dispatch_proc.h"
+
+#include <thread>
+
+static DawnProcTable nullProcs;
+thread_local DawnProcTable perThreadProcs;
+
+void dawnProcSetPerThreadProcs(const DawnProcTable* procs) {
+    if (procs) {
+        perThreadProcs = *procs;
+    } else {
+        perThreadProcs = nullProcs;
+    }
+}
+
+static WGPUProc ThreadDispatchGetProcAddress(WGPUDevice device, const char* procName) {
+    return perThreadProcs.getProcAddress(device, procName);
+}
+
+static WGPUInstance ThreadDispatchCreateInstance(WGPUInstanceDescriptor const * descriptor) {
+    return perThreadProcs.createInstance(descriptor);
+}
+
+{% for type in by_category["object"] %}
+    {% for method in c_methods(type) %}
+        static {{as_cType(method.return_type.name)}} ThreadDispatch{{as_MethodSuffix(type.name, method.name)}}(
+            {{-as_cType(type.name)}} {{as_varName(type.name)}}
+            {%- for arg in method.arguments -%}
+                , {{as_annotated_cType(arg)}}
+            {%- endfor -%}
+        ) {
+            {% if method.return_type.name.canonical_case() != "void" %}return {% endif %}
+            perThreadProcs.{{as_varName(type.name, method.name)}}({{as_varName(type.name)}}
+                {%- for arg in method.arguments -%}
+                    , {{as_varName(arg.name)}}
+                {%- endfor -%}
+            );
+        }
+    {% endfor %}
+{% endfor %}
+
+extern "C" {
+    DawnProcTable dawnThreadDispatchProcTable = {
+        ThreadDispatchGetProcAddress,
+        ThreadDispatchCreateInstance,
+{% for type in by_category["object"] %}
+    {% for method in c_methods(type) %}
+        ThreadDispatch{{as_MethodSuffix(type.name, method.name)}},
+    {% endfor %}
+{% endfor %}
+    };
+}