This will allow us to verify individual attributes.
We need this to test cached attributes like scroll position, transform matrix, etc. essentially, any cached attr that doesn't have a direct mapping between it and an accessible attribute.
We should still validate that clients get the correct composite info (ie. bounds, for scroll position and transform matrix) but this will help us test at a finer granularity.

Backed out for causing build bustages on LocalAccessible.cpp. So far it only affected Linux x64 debug.

Push with failures

Failure log Bb build
Failure log H(hazard build) build

Backout link

[task 2022-03-12T10:16:11.888Z] 10:16:11     INFO -  gmake[4]: Entering directory '/builds/worker/workspace/obj-build/accessible/generic'
[task 2022-03-12T10:16:11.890Z] 10:16:11     INFO -  /builds/worker/fetches/sccache/sccache /builds/worker/fetches/gcc/bin/g++ --sysroot /builds/worker/fetches/sysroot-x86_64-linux-gnu -std=gnu++17 -isystem /builds/worker/fetches/sysroot-x86_64-linux-gnu/usr/include/c++/7.5.0 -isystem /builds/worker/fetches/sysroot-x86_64-linux-gnu/usr/include/x86_64-linux-gnu/c++/7.5.0 -isystem /builds/worker/fetches/sysroot-x86_64-linux-gnu/usr/include/x86_64-linux-gnu -isystem /builds/worker/fetches/sysroot-x86_64-linux-gnu/usr/include -o Unified_cpp_accessible_generic0.o -c  -I/builds/worker/workspace/obj-build/dist/stl_wrappers -I/builds/worker/workspace/obj-build/dist/system_wrappers -include /builds/worker/checkouts/gecko/config/gcc_hidden.h -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector-strong -DDEBUG=1 -DOS_POSIX=1 -DOS_LINUX=1 -DMOZ_HAS_MOZGLUE -DMOZILLA_INTERNAL_API -DIMPL_LIBXUL -DSTATIC_EXPORTABLE_JS_API -I/builds/worker/checkouts/gecko/accessible/generic -I/builds/worker/workspace/obj-build/accessible/generic -I/builds/worker/checkouts/gecko/accessible/base -I/builds/worker/checkouts/gecko/accessible/html -I/builds/worker/checkouts/gecko/accessible/xpcom -I/builds/worker/checkouts/gecko/accessible/xul -I/builds/worker/checkouts/gecko/dom/base -I/builds/worker/checkouts/gecko/dom/xul -I/builds/worker/checkouts/gecko/layout/generic -I/builds/worker/checkouts/gecko/layout/xul -I/builds/worker/checkouts/gecko/accessible/ipc/other -I/builds/worker/checkouts/gecko/accessible/atk -I/builds/worker/workspace/obj-build/ipc/ipdl/_ipdlheaders -I/builds/worker/checkouts/gecko/ipc/chromium/src -I/builds/worker/workspace/obj-build/dist/include -I/builds/worker/workspace/obj-build/dist/include/nspr -I/builds/worker/workspace/obj-build/dist/include/nss -DMOZILLA_CLIENT -include /builds/worker/workspace/obj-build/mozilla-config.h -Wall -Wempty-body -Wignored-qualifiers -Wpointer-arith -Wsign-compare -Wtype-limits -Wunreachable-code -Wno-invalid-offsetof -Wduplicated-cond -Wimplicit-fallthrough -Wno-error=maybe-uninitialized -Wno-error=deprecated-declarations -Wno-error=array-bounds -Wno-error=coverage-mismatch -Wno-error=free-nonheap-object -Wformat -Wformat-overflow=2 -Wno-psabi -D_GLIBCXX_USE_CXX11_ABI=0 -fno-sized-deallocation -fno-aligned-new -fno-exceptions -fPIC -fno-rtti -ffunction-sections -fdata-sections -fno-exceptions -fno-math-errno -pthread -pipe -g -freorder-blocks -Os -fno-omit-frame-pointer -funwind-tables -Werror -fno-strict-aliasing  -MD -MP -MF .deps/Unified_cpp_accessible_generic0.o.pp   Unified_cpp_accessible_generic0.cpp
[task 2022-03-12T10:16:11.890Z] 10:16:11     INFO -  In file included from Unified_cpp_accessible_generic0.cpp:65:0:
[task 2022-03-12T10:16:11.890Z] 10:16:11     INFO -  /builds/worker/checkouts/gecko/accessible/generic/LocalAccessible.cpp: In member function 'already_AddRefed<mozilla::a11y::AccAttributes> mozilla::a11y::LocalAccessible::BundleFieldsForCache(uint64_t, mozilla::a11y::CacheUpdateType)':
[task 2022-03-12T10:16:11.890Z] 10:16:11    ERROR -  /builds/worker/checkouts/gecko/accessible/generic/LocalAccessible.cpp:3267:19: error: unused variable 'frame' [-Werror=unused-variable]
[task 2022-03-12T10:16:11.890Z] 10:16:11     INFO -       if (nsIFrame* frame = GetFrame()) {
[task 2022-03-12T10:16:11.891Z] 10:16:11     INFO -                     ^~~~~
[task 2022-03-12T10:16:11.891Z] 10:16:11     INFO -  cc1plus: all warnings being treated as errors
[task 2022-03-12T10:16:11.891Z] 10:16:11    ERROR -  gmake[4]: *** [/builds/worker/checkouts/gecko/config/rules.mk:660: Unified_cpp_accessible_generic0.o] Error 1
[task 2022-03-12T10:16:11.891Z] 10:16:11     INFO -  gmake[4]: Leaving directory '/builds/worker/workspace/obj-build/accessible/generic'
[task 2022-03-12T10:16:11.891Z] 10:16:11    ERROR -  gmake[3]: *** [/builds/worker/checkouts/gecko/config/recurse.mk:72: accessible/generic/target-objects] Error 2
[task 2022-03-12T10:16:11.891Z] 10:16:11     INFO -  gmake[3]: *** Waiting for unfinished jobs....
[task 2022-03-12T10:16:11.891Z] 10:16:11     INFO -  gmake[4]: Entering directory '/builds/worker/workspace/obj-build/config/external/icu/i18n'

https://hg.mozilla.org/mozilla-central/rev/662a4b8be720