fix(esp_log): add Kconfig to optionally bypass esp_rom_vprintf

In Log V2, ESP_LOG macros are using the runtime
constrained-environment path in esp_log_vprintf() reference
esp_rom_vprintf as the fallback formatter. On chips where ets_vprintf
is not in ROM (all targets except ESP32-S2 and ESP32-C2), this pulls
~1.2 KB of printf implementation into IRAM.

Add a new Kconfig option LOG_API_CONSTRAINED_ENV_SAFE (default y) that
controls whether this IRAM-resident fallback is used:

Also update the logging and RAM-usage documentation accordingly.

Closes https://github.com/espressif/esp-idf/issues/18346

docs/en/api-guides/performance/ram-usage.rst

@@ -194,6 +194,7 @@ The following options will reduce IRAM usage of some ESP-IDF features:
     - Disable :ref:`CONFIG_LIBC_LOCKS_PLACE_IN_IRAM` if no ISRs that run while cache is disabled (i.e. IRAM ISRs) use libc lock APIs.
     :CONFIG_ESP_ROM_HAS_SUBOPTIMAL_NEWLIB_ON_MISALIGNED_MEMORY: - Disable :ref:`CONFIG_LIBC_OPTIMIZED_MISALIGNED_ACCESS` to save approximately 1000 bytes of IRAM, at the cost of reduced performance.
     :SOC_SPIRAM_SUPPORTED: - Enable :ref:`CONFIG_ESP_EVENT_LOOP_IN_EXT_RAM` to force ``esp_event`` to place event loop related allocations in external RAM instead of internal RAM.
+    :not CONFIG_ESP_ROM_HAS_VPRINTF_FUNC: - When using **Log V2**, disable :ref:`CONFIG_LOG_API_CONSTRAINED_ENV_SAFE` to remove ``esp_rom_vprintf`` from IRAM, saving ~1.2 KB. This means ``ESP_LOGx`` will no longer safely fall back to ROM-based printing in ISRs or with cache disabled. Use ``ESP_DRAM_LOGx`` explicitly for constrained-environment logging. See :doc:`/api-reference/system/log` for details.
 
 .. only:: esp32