Fix console aliases not working

[lhecker]

#14745 contains two regressions related to console alias handling:

• When ProcessAliases expands the backup buffer into (an) aliased
  command(s) it changes the _bytesRead field of COOKED_READ_DATA,
  requiring us to re-read it and reconstruct the input string-view.
• Multiline aliases are read line-by-line whereas Remove TranslateUnicodeToOem and all related code #14745 didn't treat
  them any different from regular single-line inputs.

Validation Steps Performed

In cmd.exe run

doskey test=echo foo$Techo bar$Techo baz
test

The output should look exactly like this:

C:\>doskey test=echo foo$Techo bar$Techo baz

C:\>test
foo

C:\>bar

C:\>baz

C:\>

[lhecker]

Another one down the list #14298.

[lhecker]

This isn't necessarily the most readable code I've written so far... But it does do the correct thing: After Consume() returns, input might not be empty! So if we restore the original, full input slice we need to manually calculate the amount of data that was read (amountConsumed).

An alternative I've considered is to change Consume() to return the amount of characters that were read, but given how Consume() works internally, this would be identical to this inputSizeBefore / inputSizeAfter code. Alternatively we could pass a "character limit" argument, but that would be, once again, similar to the existing code, since string-views are already strings with a limit, so I felt like passing 2 limits wouldn't be any less confusing.

[lhecker]

This code block is identical to the other one, but it's shorter because we can easily access the previously saved pending slice.

[zadjii-msft]

@miniksa thanks for selfhosting 😉

[DHowett]

Okay, this makes some sense to me.

[DHowett]

I have to trust, to some extent, the code here. I understand it but only to a point. :D

[carlos-zamora]

Good callout!