Preserve is_email_receipt parameter through to email sent

Following from CRM-19601, the is_email_receipt parameter still gets overridden later down the chain again.

For example, this scenario:

1. Contribution page sets "Email Receipt to Contributor? = FALSE", so "is_email_receipt => 0"
2. Contribution made at status Pending
3. API call to completetransaction sets "is_email_receipt => 1" (i.e. send the receipt on completion regardless of Contribution page setting)
4. completetransaction calls completeOrder(), which calls sendconfirmation API call - is_email_receipt isn't passed along
5. sendconfirmation calls sendMail, which calls composeMessageArray()
6. composeMessageArray() gets settings by "$this->_gatherMessageValues($input, $values, $ids)", which has "is_email_receipt => 0" (the setting provided by the Contribution page)
7. No email is sent, the override was ignored/lost

For Events, is_email_receipt can be fed through completetransaction, but no confirmation email is sent even if "is_email_receipt => 1", because is_email_confirm isn't set at the same time.

PRs built off CRM-19601 to fix these cases coming through.

Agileware Ref #24374