fix(file_system): rename esp_littlefs submodule to littlefs so dependency name is always the same

[finger563]

Description

• Update file_system/CMakeLists.txt to have littlefs be the dependency name, since that is what it will be when used as a managed component
• Update esp_littlefs submodule to be named littlefs so that it matches the managed component behavior.

Motivation and Context

It was found in testing that the file_system component failed to buid when used as a managed component because the littlfs dependency comes in under the name littlefs, but the repo was originally designed to use esp_littlefs.

Note: I tried initially to add the following code to the file system cmake, but it didn't work in the case that IDF_COMPONENT_MANAGER=0 when building:

# Determine whether file_system is fetched from component registry or from local path
idf_build_get_property(build_components BUILD_COMPONENTS)
if(file_system IN_LIST build_components)
    set(required_littlefs_name esp_littlefs) # Local component
else()
    set(required_littlefs_name littlefs) # Managed component
endif()

How has this been tested?

• Build and run in a managed component test project.
• Build and run file_system/example (not managed component) (IDF_COMPONENT_MANAGER=0 idfb)
• Build and run file_system/example (managed component) (idfb)

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Hardware (schematic, board, system design) change
• Software change

Checklist:

• My change requires a change to the documentation.
• I have added / updated the documentation related to this change via either README or WIKI

Software

• I have added tests to cover my changes.
• I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• All new and existing tests passed.
• My code follows the code style of this project.

[github-actions]

✅Static analysis result - no issues found! ✅