starboard: Replace URL player config macro with tvOS buildflag

[abhijeetk]

SB_HAS_PLAYER_WITH_URL is legacy Cobalt configuration that was only
defined for tvOS in configuration_public.h. In the Chromium
architecture, BUILDFLAG(IS_IOS_TVOS) is the standard way to gate
tvOS-specific code.

Replace all SB_HAS(PLAYER_WITH_URL) guards with BUILDFLAG(IS_IOS_TVOS)
across sbplayer_bridge, sbplayer_interface, starboard_renderer, and
url_player_create_test. Replace the indirect SB_URL_PLAYER_INCLUDE_PATH
include with the direct header path. Remove both definitions from
starboard/tvos/shared/configuration_public.h.

Required-For: #10698

Bug: 512045535

[github-actions]

🤖 Gemini Suggested Commit Message

---

starboard: Use BUILDFLAG for tvOS URL player

Replace the legacy SB_HAS_PLAYER_WITH_URL configuration with the
standard BUILDFLAG(IS_IOS_TVOS) to gate tvOS-specific URL player code.
This aligns Starboard with the standard Chromium architecture.

Additionally, replace the indirect SB_URL_PLAYER_INCLUDE_PATH macro
with direct header includes and remove the obsolete definitions from
the tvOS shared configuration headers.

Bug: 512045535

---

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[abhijeetk]

cc : @Gyuyoung @jkim-julie @rakuco

[gemini-code-assist]

Code Review

This pull request replaces the generic SB_HAS(PLAYER_WITH_URL) preprocessor macro with the platform-specific BUILDFLAG(IS_IOS_TVOS) across several media and Starboard files, and cleans up the associated configurations. Feedback suggests forward-declaring SbUrlPlayerExtraInfo in sbplayer_interface.h to avoid platform-specific headers in generic interfaces, and points out that including tvOS-specific headers in the generic NPLB test suite violates its platform-agnostic design.

[abhijeetk]

This PR implements the changes as per review comment on PR 10698