Update builder API to use grpc-swift-2. (#1309) (#1416)

- Closes #1308.
- Applies dependency and code changes similar to
apple/containerization#578.
- Upgrades hawkeye to latest version.
- Update StderrLogHandler not to create a (non-Sendable) Swift time
formatter object for every log message.

scripts/install-hawkeye.sh

@@ -17,6 +17,6 @@ if command -v .local/bin/hawkeye >/dev/null 2>&1; then
     echo "hawkeye already installed"
 else
     echo "Installing hawkeye"
-    export VERSION=v6.1.0
+    export VERSION=v6.5.1
     curl --proto '=https' --tlsv1.2 -LsSf https://github.com/korandoru/hawkeye/releases/download/${VERSION}/hawkeye-installer.sh | CARGO_HOME=.local sh -s -- --no-modify-path
 fi