Reevaluate spoken forms for triple surrounding pairs

[phillco]

https://github.com/cursorless-dev/cursorless/pull/2775/files adds triple ` as a supported surrounding pair, and adds a private spoken form, but not one that the user will be able to use by default.

It's probably useful to be able to target these in Markdown files since they are likely distinct blocks (you could have some other pair inside of a code block inside of a markdown file. grand pair works but requires more thinking).

Same with very large multiline strings in Python - as the string gets larger and potentially contains other strings it's nice to be able to target the entire thing.

Probably worth considering just adding spoken forms for all three.