common fixes for guava_version_upgrade

[AbhishekKumar9984]

Replace removed APIs:

Throwables.propagate() -> throw new RuntimeException(e)
InputSupplier (removed) -> use existing ContentProvider
Charsets.UTF_8 -> StandardCharsets.UTF_8
Objects.toStringHelper/firstNonNull -> MoreObjects equivalents
Objects.hashCode -> java.util.Objects.hash
startAndWait/stopAndWait -> startAsync().awaitRunning/stopAsync().awaitTerminated
Update ASM bytecode generation to use RuntimeException constructor
Fix header ordering in HttpRequestsTestBase

[gemini-code-assist]

Code Review

This pull request upgrades the Guava library to version 32.0.0-jre and refactors the codebase to replace deprecated or internal Guava utilities with standard Java APIs or modern Guava alternatives. Key changes include migrating from com.google.common.base.Charsets to java.nio.charset.StandardCharsets, replacing com.google.common.base.Objects with java.util.Objects or com.google.common.base.MoreObjects, and substituting Throwables.propagate with standard RuntimeException wrapping. Feedback suggests improving the ASM bytecode generation in FieldAccessorGenerator.java by using a more general exception type for local variables and simplifying the instruction sequence for exception instantiation.