Assert that a sequence of strings appears on the page in a given order

Problem/Motivation

#2757007: Convert all book web tests to BrowserTestBase uses a method for this, but I believe it should be added to WebAssert. I've already seen similar implementations in contrib.

Proposed resolution

Add the method to WebAssert.

Remaining tasks

• Search for @todos connected with this issue and update to use new assertions.

User interface changes

API changes

Testing additions.

Data model changes