chore(deps): upgrade gapic-generator-java to 2.8.0 and update gax-java to 2.18.1 (#357)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 450543911

Source-Link: googleapis/googleapis@5528344

Source-Link: https://github.com/googleapis/googleapis-gen/commit/9f6775cab1958982b88967a43e5e806af0f135db
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiOWY2Nzc1Y2FiMTk1ODk4MmI4ODk2N2E0M2U1ZTgwNmFmMGYxMzVkYiJ9

Author: gcf-owl-bot[bot]

java-area120-tables/google-area120-tables/src/main/java/com/google/area120/tables/v1alpha/TablesServiceClient.java

@@ -158,7 +158,6 @@ public static final TablesServiceClient create(TablesServiceSettings settings)
    * Constructs an instance of TablesServiceClient, using the given stub for making calls. This is
    * for advanced usage - prefer using create(TablesServiceSettings).
    */
-  @BetaApi("A restructuring of stub classes is planned, so this may break in the future")
   public static final TablesServiceClient create(TablesServiceStub stub) {
     return new TablesServiceClient(stub);
   }
@@ -173,7 +172,6 @@ protected TablesServiceClient(TablesServiceSettings settings) throws IOException
     this.stub = ((TablesServiceStubSettings) settings.getStubSettings()).createStub();
   }
 
-  @BetaApi("A restructuring of stub classes is planned, so this may break in the future")
   protected TablesServiceClient(TablesServiceStub stub) {
     this.settings = null;
     this.stub = stub;
@@ -183,7 +181,6 @@ public final TablesServiceSettings getSettings() {
     return settings;
   }
 
-  @BetaApi("A restructuring of stub classes is planned, so this may break in the future")
   public TablesServiceStub getStub() {
     return stub;
   }

java-area120-tables/google-area120-tables/src/main/java/com/google/area120/tables/v1alpha/stub/TablesServiceStubSettings.java

@@ -364,7 +364,6 @@ public UnaryCallSettings<BatchDeleteRowsRequest, Empty> batchDeleteRowsSettings(
     return batchDeleteRowsSettings;
   }
 
-  @BetaApi("A restructuring of stub classes is planned, so this may break in the future")
   public TablesServiceStub createStub() throws IOException {
     if (getTransportChannelProvider()
         .getTransportName()