build: Overlay build vars expand ${ZEPHYR_<module>_MODULE_DIR}

[gregshue]

Support referencing module directories by name in CONF_FILE,
OVERLAY_CONFIG, and DTC_OVERLAY_FILE so that projects can reference
overlay files in arbitrary modules.

Fixes #41830

Signed-off-by: Gregory Shue [email protected]

[gregshue]

Updated version of automatically closed PR #42057

[tejlmand]

Please push the correct and approved version.

Current version is older with unaddressed comments.

[tejlmand]

Could you please push the correct version ?

This is old version where changes was requested here:
#42057 (comment)

note you most likely need to manually expand collapsed comments in github for the link to take you to the right comment.
Old comment copy:

Looking at the rendered output, I feel this particular feature fills to much, compared to the description of the other parts:

How about just a short mentioning of this possibility, for example:

Suggested change

	set(CONF_FILE "\${ZEPHYR_MODULENAME_MODULE_DIR}/<module-relative-pathname>")
	``DTC_OVERLAY_FILE``. A file in a Zephyr module can be referred by escaping the Zephyr module dir variable like this ``\${ZEPHYR_<module>_MODULE_DIR}/<path-to>/<file>`` when setting any of said variables.

[gregshue]

@tejlmand Thank you for pointing out my mistake. I have corrected the changes that I could map to the current files. Some of the relevant documentation has been restructured. I will need some guidance on further documentation updates.

[tejlmand]

lgtm

[gregshue]

Rebased, updated test source to new ZTest API.