fix #3855: (http-support): correct native request builder URI/body/header sem…

[YianZhao]

Summary

This PR fixes request-construction semantics in the native HTTP client path (newHttpClientAlt) by updating NewRequestBuilderImpl.

What was wrong

NewRequestBuilderImpl had three behavior issues:

1. Invalid URIs were silently ignored.
2. Requests without an explicit body could be built through a null-body path.
3. Content-Type: application/json was forced for all requests in build().

These behaviors are inconsistent with expected HTTP request semantics and can produce incorrect requests.

Changes

Code changes

• Updated uri(String uri) to use URI.create(uri) directly, so invalid URIs fail fast with IllegalArgumentException.
• Updated build() to use BodyPublishers.noBody() when no body is provided.
• Removed unconditional Content-Type: application/json injection from build().

Tests added

Added new unit test class:

• NewRequestBuilderImplTest

Covered scenarios:

• invalid URI is rejected,
• GET without body builds successfully and does not set forced content type,
• POST without body builds successfully and does not set forced content type,
• explicitly set Content-Type is preserved and not overridden.

Verification

Executed:

mvn -pl clients/http-support "-Dbase.deploy.dir=." "-DskipTests=false" "-Dmaven.test.skip=false" "-Dtest=NewRequestBuilderImplTest" test

[YianZhao]

Thanks for taking a look. All checks are passing on my side now. Please let me know if any changes are needed when you review it.