Using addAtMain stopped working for programs without main functions
(HAS_MAIN not defined) after #13901.

Code that needs to populate the FS is mostly likely going to be run
during preRun callback which all happen before ATINITs.

Using addAtMain stopped working for programs without main functions
(HAS_MAIN not defined) after #13901.

Code that needs to populate the FS is mostly likely going to be run
during preRun callback which all happen before ATINITs.

Using addAtMain stopped working for programs without main functions
(HAS_MAIN not defined) after #13901.

Code that needs to populate the FS is mostly likely going to be run
during preRun callback which all happen before ATINITs.

Using addAtMain stopped working for programs without main functions
(HAS_MAIN not defined) after #13901.

Code that needs to populate the FS is mostly likely going to be run
during preRun callback which all happen before ATINITs.

This reduces code size and prevents accidental/confusing use of these
elements, which don't have any meaning without a main function.

Since #13901 they have been in-active in application without a main
export.

Might help with #14583.

Support for `addAtMain` in application without a main function was
removed in #13901 but I missed that fact that webidl_binder.py was doing
this.

This change replaces `addAtMain` with `addOnInit` and also makes the use
of `addAtMain` in applications withoiut a `main` into an error so that
the problem (and solution) should be clear.

Update webidl binder test to only use sync compilation when needed, so
that code in question actually gets tested.

This change also reduces code size by not including `addAtMain` at all
in applcications without a `main`.

Fixes: #14583.

Support for `addAtMain` in application without a main function was
removed in #13901 but I missed that fact that webidl_binder.py was doing
this.

This change replaces `addAtMain` with `addOnInit` and also makes the use
of `addAtMain` in applications withoiut a `main` into an error so that
the problem (and solution) should be clear.

Update webidl binder test to only use sync compilation when needed, so
that code in question actually gets tested.

This change also reduces code size by not including `addAtMain` at all
in applcications without a `main`.

Fixes: #14583.

Support for `addAtMain` in application without a main function was
removed in #13901 but I missed that fact that webidl_binder.py was doing
this.

This change replaces `addAtMain` with `addOnInit` and also makes the use
of `addAtMain` in applications without a `main` into an error so that
the problem (and solution) should be clear.

Update webidl binder test to only use sync compilation when needed, so
that code in question actually gets tested.

This change also reduces code size by not including `addAtMain` at all
in applications without a `main`.

Fixes: #14583.