Correct documentation of trigger firing order

[mrotteveel]

Currently, the documentation of trigger firing order in the various language references incorrectly state that firing order for the same position is alphabetical. It is not, it is undefined.

This needs to be fixed in fblangref25 - fblangref50.

[mrotteveel]

See also FirebirdSQL/firebird#8275

[mrotteveel]

Will publish later, after more changes have accumulated