Move test demo apps out of Bazel to ease Go version deprecation and support testing offsetgen instrumentation #2650

Job	Run time
env-protect-setup	6s
authorize	3s
get-dev-image / get-image	6s
clang-tidy	6m 47s
generate-matrix	24m 8s
code-coverage	0s
build-and-test (BPF opt (4.14.254), kvm, --config=qemu-bpf --compilation_mode=opt --//bazel/test_...	17m 14s
build-and-test (BPF opt (6.1.106), kvm, --config=qemu-bpf --compilation_mode=opt --//bazel/test_r...	20m 31s
build-and-test (ASAN, nokvm, --config=asan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	16m 7s
build-and-test (Clang opt + UI, nokvm, --config=clang --compilation_mode=opt, bazel_buildables_cl...	15m 56s
build-and-test (Clang debug, nokvm, --config=clang --compilation_mode=dbg, bazel_buildables_clang...	16m 2s
build-and-test (Go race detector, nokvm, --config=go_race --compilation_mode=opt, bazel_buildable...	12m 30s
build-and-test (TSAN, nokvm, --config=tsan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	15m 58s
build-and-test (GCC opt, nokvm, --config=gcc --compilation_mode=opt, bazel_buildables_gcc_opt, ba...	16m 9s
build-and-test-status	3s
	2h 41m 40s

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