fuchsia-build: Update Fuchsia SDK and deps, API level 30 Added update steps to README.md Bug:512999679 Change-Id: I4155787d46d76911e16b7e93f4d17638677fdaac Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1611276 Commit-Queue: Craig Stout <cstout@google.com> Reviewed-by: David Gilhooley <dgilhooley@google.com>