Editorial: Unify 'else' and 'otherwise'

[jungwngkim]

This PR implements points discussed in issue #3648

Although I've tried to replace every occurrence of 'otherwise' with 'else' in the algorithm steps, there were 16 cases where simply replacing with 'else' lead to awkward sentence. I listed them below.

$ grep "1\. .* otherwise" spec.html -n
(...) the host is a web browser or otherwise supports <emu-xref> # 11 cases
(...) if _Desc_ has that field, or to the attribute's <emu-xref>default value</emu-xref> otherwise. # 4 cases
NOTE: (...) unless specified otherwise. # 1 case

[michaelficarra]

Surely we can just say Return *false*. here.

Suggested change

	1. Else, return *false*.
	1. Return *false*.

[michaelficarra]

@tc39/ecma262-editors For the single-line if/else where both branches return, do we want to just split them up into two steps?