[bazel] Housekeeper-PerCommit-GoLinters: Add errcheck step.

This CL adds an "errcheck" step to go_linters.go, which is based on Skia Infrastructure's errcheck step here: https://skia.googlesource.com/buildbot/+/0d2306dfb51e596840725bc22674f938aa29aeb4/infra/bots/task_drivers/bazel_build_all/bazel_build_all.go#83. Same for //infra:errcheck.

File hello_world.go was moved to a directory without any C++ files to prevent the following errcheck error:

    C++ source files not allowed when not using cgo or SWIG: bazel_test.cpp pathop_main.cpp

All other Go changes are manual edits to appease errcheck by explicitly ignoring all errors returned by functions ("_ = foo()" rather than just "foo()"), with the following exceptions, where I tried to actually handle the errors:

- //infra/bots/task_drivers/recreate_skps/recreate_skps.go
- //tools/unicode_comparison/go/extract_info/main.go

Bug: b/40045301
Change-Id: Id4f4c80239acf4af945565e1e4b68c367700058d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/778340
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
14 files changed