[urlrewrite] Minor edits

[joewiz]

• the /tools root is no longer in eXist
• the sandbox tool is no longer in eXist; adapted to discuss eXide
• added a few essential details to the picture of URL processing and controller-config
• incorporate recent changes to roots in Improve controller-config inline comments exist#4807
• reorder $exist:* variables from most general to most specific components
• add descriptions of common uses of URL rewriting

[joewiz]

(I rebased this PR after merging #903, but CI tests are still failing on this PR. The tests in README.md - mvn validate, mvn test, and npm run cypress - all pass locally on my system.)

[line-o]

These changes are a big step forward for new users to understand the URL rewriting.
Many thanks.
I found some typos and have some questions. These can all be addressed at a later point if you do not feel they are urgent.

[duncdrum]

@joewiz does this need a rebase, or have these changes already been incorporated ?

[joewiz]

@duncdrum It needs a rebase. Coming...

[duncdrum]

Nice improvements. @line-o comments are still unresolved. I added a few stylistic notes. We should be consistent in the use of $ when referring to Xquery variable names.

[duncdrum]

@joewiz could you have a look at @line-o and my comments, and see which ones you can implement and which require more input?

[joewiz]

@line-o @duncdrum Thanks for your comments! I've incorporated them in my most recent commit.

[duncdrum]

@line-o lets tackle #940 in a separate PR.
@joewiz one last suggestion for you to accept or not. Otherwise this is good to merge.