Remove the CFG_TUSB_RHPORTx_MODE fallback and tusb_init(void); rename TUP_RHPORT_HIGHSPEED #4501

Deferred from #3779. CFG_TUSB_RHPORT0_MODE / CFG_TUSB_RHPORT1_MODE were superseded in 0.14.0 by CFG_TUD_ENABLED / CFG_TUH_ENABLED and CFG_TUD_MAX_SPEED / CFG_TUH_MAX_SPEED (docs/changelog/0.14.0.md:19), and tusb_init(void) was deprecated in 0.18.0 (docs/changelog/0.18.0.md:16). Both are still supported as fallbacks.

Scope

• Remove the CFG_TUSB_RHPORTx_MODE fallback in src/tusb_option.h:489-506 (device) and :531-548 (host): TUD_RHPORT_MODE, TUH_RHPORT_MODE, and the CFG_TUD_ENABLED / CFG_TUD_MAX_SPEED / CFG_TUH_ENABLED / CFG_TUH_MAX_SPEED defaults derived from them.
• tusb_init(void): its rhport comes only from TUD_OPT_RHPORT / TUH_OPT_RHPORT, which only CFG_TUSB_RHPORTx_MODE defines (src/tusb.h:143-146, src/tusb.c:66-86). Decide whether to remove it (calls fail at compile time with a pointer to tusb_init(rhport, &init)) or give it another rhport source.
• Migrate the in-tree users:
  • lib/rt-thread/tusb_config.h:90-93, 156-157 sets CFG_TUSB_RHPORT0/1_MODE; lib/rt-thread/tusb_rt_thread_port.c:61 calls tusb_init().
  • test/unit-test/test/support/tusb_config.h.
  • Comment in src/portable/bridgetek/ft9xx/dcd_ft9xx.c:305.
• Rename the high-speed port default the way Add USB SuperSpeed (USB 3.2) device support with WCH CH569 and CH32H417 ports #3779 renamed the SuperSpeed one (TUP_RHPORT_SUPERSPEED -> CFG_TUSB_SUPER_SPEED_DEFAULT, resolved to the overridable CFG_TUSB_SUPER_SPEED): TUP_RHPORT_HIGHSPEED -> CFG_TUSB_HIGH_SPEED_DEFAULT / CFG_TUSB_HIGH_SPEED, shared by TUD_OPT_HIGH_SPEED and TUH_OPT_HIGH_SPEED (src/tusb_option.h:515, 555), including the unit-test definitions (test/unit-test/project.yml:158, test/unit-test/CMakeLists.txt:160). Keep the SuperSpeed-implies-HighSpeed rule of TUD_OPT_HIGH_SPEED.
• Changelog entry: breaking change for applications still using CFG_TUSB_RHPORTx_MODE or tusb_init(void).

Why deferred

It is a breaking change for every application on the old configuration and unrelated to the SuperSpeed ports in #3779. Out-of-tree users (Arduino, ESP-IDF components, vendor SDKs) are not surveyed yet.