Support setting the local address per connection with ConnectOptions

[jnbdz]

Motivation

TCP based clients can only bind their connections to the local address configured at the client level; binding a given connection to a specific interface or port requires a dedicated client. This implements the approach discussed in #2335: the local address is a per-connection property, the client-level value is only a default.

Fixes #2335.

Changes

Following the steps listed in the issue:

1. localAddress is removed from TcpClientConfig — ⚠️ note that TcpClientConfig#setLocalAddress was released in 5.1.x, so this is an API removal on 5.2; if you would rather keep it as @Deprecated and ignored for one release, I can adjust.
2. the client default local address is now held by NetClientImpl and set by NetClientBuilder, from the legacy NetClientOptions#setLocalAddress(String) (NetClientBuilder#localAddress(ClientOptionsBase) does the mapping to an inet socket address with an ephemeral port).
3. localAddress is added as a SocketAddress on ConnectOptions (domain socket addresses are rejected), and on HttpConnectOptions too since it does not extend ConnectOptions.
4. at connect time, ConnectOptions#getLocalAddress() is used when set, otherwise the client default (which may be null).
5. the resulting local address is set on the Bootstrap.

For the HTTP client, HttpClientImpl#connect(HttpConnectOptions) propagates the local address through HttpConnectParams to TcpHttpClientTransport, so an un-pooled connection can be bound to a local address; pooled requests keep using the client default. The QUIC transport is unchanged (it has its own configuration).

Legacy HTTP / WebSocket client local address was ignored

While wiring this I found that HttpClientOptions#setLocalAddress and WebSocketClientOptions#setLocalAddress were silently ignored on 5.x: HttpClientConfig(HttpClientOptions) goes through TcpClientConfig(ClientOptionsBase), which never copied the local address (only the NetClientOptions constructor did). With setLocalAddress("127.0.0.2") the server saw connections from 127.0.0.1. The existing HttpTest#testClientLocalAddress did not catch it because it binds to and asserts 127.0.0.1. This is fixed by passing the legacy options local address to NetClientBuilder in HttpClientBuilderInternal and in VertxImpl#createWebSocketClientImpl.

Tests

• NetTest#testConnectOptionsLocalAddress: connect with ConnectOptions#setLocalAddress bound to a specific free port, assert the server sees that source port and NetSocket#localAddress() reports it.
• NetTest#testConnectOptionsLocalAddressOverridesClientLocalAddress: the client is created with NetClientOptions#setLocalAddress, the connect options local address takes precedence.
• Http1xTest#testConnectOptionsLocalAddress: same through HttpClient#connect(HttpConnectOptions).
• Http1xTest#testClientOptionsLocalAddress: legacy HttpClientOptions#setLocalAddress("127.0.0.2") is honoured (skipped with Assume on platforms without that loopback address).
• The existing NetTest#testClientLocalAddress / HttpTest#testClientLocalAddress keep passing.

Documentation: a paragraph and example in the TCP client section (connectingToAServerFromALocalAddress).

NetTest, Http1xTest, Http2Test, WebSocketTest, the proxy tests, SharedHttpClientTest and the net/options test packages pass locally.