Bazel (#4636)
* Replace tensorflow with a bazel external repository
* Basic migration to bazel for xla_client.
* Revert to blob
* Add vscode config.
* Update newlines
* Merge with pjrt client test build changes.
* Migrate tests to new build
* Format test and plugin
* Order imports
* Conditionally apply tf patches; apply pt patches always.
* Format python
* configure formatters
* Mirror TF pin update an fixes in bazel.
* Support local and sandboxed build based on flags
* Add cloud cache URLs for llvm.
* Merge with upstream
* Update TF pin
* Fix patching regression
* Remove the citcleci setup downloading llvm
* Rework the experimental dockerfile for bazel support
