Fix some things for extract component

[ryzngard]

Extract component had some odd behavior around MarkupTextLiteralSyntax selection.

Previously it would not allow a user to have a text literal as the start or end of the selection, it would always try to get the parent block. That works as intended for most cases where a user is highlighting inside a tag and the tag shouldn't be split. However, if the text is top level in the document it won't have a parent tag and thus would not have been considered a valid selection. This allows for that scenario.

There was also an issue if the selection was following a tag with a sibling text literal. If the selection ended after the brace but the text literal was not empty the selection would fail. For example:

[|<h1>Hello</h1>|]

Welcome to your new app

In the above the end of the selection is in the MarkupTextLiteralSyntax when it should be on the h1 node. A check for if the position was at the beginning of a text literal and it has a previous sibling was added to account for this.

[davidwengier]

I think the logic in general here is starting to get convoluted. I don't think thats necessarily wrong, as I expect there to be edge cases and weirdness, and if we have decent tests (which we pretty much do) then I'm okay with it, but I think it wouldn't be bad to overcompensate this code with comments.

[ryzngard]

@davidwengier I tried to add more comments, clean up the logic, and added a few more test for cases. Enough has changed it's probably worth a re-review

[davidwengier]

Love your work