Use GAX instead of the custom SpannerImpl.runWithRetries method for retrying server calls.

This migration involves three changes:

• Remove the override of the generated default settings in GapicSpannerRpc that set the retryable error codes to an empty set. This will automatically enable GAX retries for all server calls using the default values that have already been defined. The defaults are the same as the defaults that are used by SpannerClient.
• Add configuration options to SpannerOptions to allow the user to change the default RetrySettings. As SpannerOptions is used to create a Spanner instance, which again contains both a DatabaseClient, DatabaseAdminClient and InstanceAdminClient, SpannerOptions must contain configuration options for all three underlying clients.
• The runWithRetries method in SpannerImpl is removed and all references to it changed into direct calls that will automatically be retried by GAX.

To avoid a lot of unnecessary configuration options on SpannerOptions, the retry settings of the three underlying clients are exposed by exposing the StubSettings.Builders that are used to create the underlying clients. This only adds three extra methods to SpannerOptions, while still granting (advanced) users access to all configuration options.

The client library will use the defaults that are globally defined for retries in the configuration yaml files of Spanner (i.e. in the files spanner_gapic.yaml, spanner_admin_database_gapic.yaml and spanner_admin_instance_gapic.yaml)

The following defaults are defined:

• Spanner default settings:
  • Initial retry delay: 1 second
  • Retry multiplier: 1.3
  • Max retry delay: 32 seconds
  • Initial RPC timeout: 60 seconds
  • RPC timeout multiplier: 1.0
  • Max RPC timeout: 60 seconds
  • Total timeout: 600 seconds
• Spanner streaming settings (used for executeStreamingSql and streamingRead):
  • Initial retry delay: 1 second
  • Retry multiplier: 1.3
  • Max retry delay: 32 seconds
  • Initial RPC timeout: 120 seconds
  • RPC timeout multiplier: 1.0
  • Max RPC timeout: 120 seconds
  • Total timeout: 1200 seconds
• Spanner long-running settings (used for commit):
  • Initial retry delay: 1 second
  • Retry multiplier: 1.3
  • Max retry delay: 32 seconds
  • Initial RPC timeout: 3600 seconds
  • RPC timeout multiplier: 1.0
  • Max RPC timeout: 3600 seconds
  • Total timeout: 3600 seconds
• Database admin default settings (used for all methods except methods that return an operation, i.e. createDatabase and updateDatabaseDdl, these have a total timeout of 24 hours):
  • Initial retry delay: 1 second
  • Retry multiplier: 1.3
  • Max retry delay: 32 seconds
  • Initial RPC timeout: 60 seconds
  • RPC timeout multiplier: 1.0
  • Max RPC timeout: 60 seconds
  • Total timeout: 600 seconds
• Instance admin default settings (used for all methods except methods that return an operation, i.e. createInstance and updateInstance, these have a total timeout of 24 hours):
  • Initial retry delay: 1 second
  • Retry multiplier: 1.3
  • Max retry delay: 32 seconds
  • Initial RPC timeout: 60 seconds
  • RPC timeout multiplier: 1.0
  • Max RPC timeout: 60 seconds
  • Total timeout: 600 seconds