fix(bootloader): handle extra component dirs in v1 subproject

Closes https://github.com/espressif/esp-idf/issues/18651

examples/custom_bootloader/bootloader_extra_dir/README.md

@@ -5,9 +5,11 @@
 
 (See the README.md file in the upper level for more information about bootloader examples.)
 
-The purpose of this example is to show how to add a custom directory that contains a component to the bootloader build.
+The purpose of this example is to show how to add bootloader components that are not placed in the conventional `bootloader_components` directory.
 
-Registering extra components for the bootloader can be done thanks to the IDF property `BOOTLOADER_EXTRA_COMPONENT_DIRS`. It can either refer to a directory that contains several components, either refer to a single component.
+The bootloader always uses the `bootloader_components` folder name as the project-local search path for bootloader components. Use this folder for bootloader-specific code that belongs to the project, such as hooks or overrides.
+
+Use the `BOOTLOADER_EXTRA_COMPONENT_DIRS` property when bootloader components already live somewhere else, for example in a shared components directory or in a component reused by several projects. Each path can point either to a directory containing multiple components or directly to a single component. If the extra location contains components that are not needed in a particular bootloader build, list them by component name in `BOOTLOADER_IGNORE_EXTRA_COMPONENT`.
 
 ## Usage of this example:
 
@@ -33,9 +35,11 @@ User application is loaded and running.
 
 ## Organization of this example
 
-This project contains a `main` directory that represents an application. It also has a `bootloader_components` directory that contains a component that will be compiled and linked with the bootloader. This `bootloader_components` can contain several components, each of them would be in a different directory.
+This project contains a `main` directory that represents an application. It also has a `bootloader_components` directory with `my_boot_hooks`, a bootloader-specific hook component that belongs to this project.
 
-The directory `extra_bootloader_components/extra_component/` contains a component that is meant to be included in the bootloader build. To do so, the CMake property `BOOTLOADER_EXTRA_COMPONENT_DIRS` is set from the `CMakeLists.txt` file.
+The `extra_bootloader_components/` directory demonstrates an extra path that contains several components. `extra_component1` is required by `my_boot_hooks`, while `extra_component2` is included directly from `BOOTLOADER_EXTRA_COMPONENT_DIRS` without being required by another component. `extra_component3` is present in the same directory but is excluded from this bootloader build with `BOOTLOADER_IGNORE_EXTRA_COMPONENT`.
+
+The `extra_component4/` and `extra_component5/` directories demonstrate extra paths that point directly to individual components. `extra_component4` is included directly, while `extra_component5` is excluded with `BOOTLOADER_IGNORE_EXTRA_COMPONENT`.
 
 Below is a short explanation of files in the project folder.
 
@@ -49,8 +53,20 @@ Below is a short explanation of files in the project folder.
 │       ├── CMakeLists.txt
 │       └── hooks.c            Implementation of the hooks to execute on boot
 ├── extra_bootloader_components
-│   └── extra_component
+│   ├── extra_component1
+│   │   ├── CMakeLists.txt
+│   │   └── extra_component1.c                 Implementation of the extra component
+│   ├── extra_component2
+│   │   ├── CMakeLists.txt
+│   │   └── extra_component2.c                 Implementation of the 2nd extra component
+│   └── extra_component3
 │       ├── CMakeLists.txt
-│       └── extra_component.c  Implementation of the extra component
+│       └── extra_component3.c                 Extra component excluded from this bootloader build
+├── extra_component4
+│   ├── CMakeLists.txt
+│   └── extra_component4.c                     Extra component included directly
+├── extra_component5
+│   ├── CMakeLists.txt
+│   └── extra_component5.c                     Extra component excluded directly
 └── README.md                  This is the file you are currently reading
 ```