app_update: Add API for getting sha256_of_partition

Added bootloader_common_get_sha256_of_partition() and esp_partition_get_sha256() - get or calculate SHA-256
digest for app and data partitions.
Added bootloader_sha256_hex_to_str() - helps to print SHA-256 digest
Added esp_partition_check_identity() - compares two partitions by SHA-256 digest

Refactoring a function esp_image_load() in bootloader space to esp_image_verify() and
bootloader_load_image(). Old name function esp_image_load is deprecated
and will remove in V4.0 version.

spi_flash/sim: Fix error test_host. Add stub for bootloader_common_get_sha256_of_partition in sim/stubs

components/bootloader_support/src/bootloader_utility.c

@@ -50,6 +50,7 @@
 #include "bootloader_config.h"
 #include "bootloader_common.h"
 #include "bootloader_utility.h"
+#include "bootloader_sha.h"
 
 static const char* TAG = "boot";
 
@@ -265,7 +266,7 @@ static bool try_load_partition(const esp_partition_pos_t *partition, esp_image_m
         return false;
     }
 #ifdef BOOTLOADER_BUILD
-    if (esp_image_load(ESP_IMAGE_LOAD, partition, data) == ESP_OK) {
+    if (bootloader_load_image(partition, data) == ESP_OK) {
         ESP_LOGI(TAG, "Loaded app from partition at offset 0x%x",
                  partition->offset);
         return true;