Overhaul JavaTemplate documentation

[knutwannheden]

As of OpenRewrite 8 the JavaTemplate API changed quite a bit and also introduces the distinction of context-free and -sensitive templates. This calls for an overhaul of the documentation on this topic.

[mike-solomon]

This issue requires the help of someone on the dev team to read through the JavaTemplate doc and then provide information on what needs to change. Tagging @sambsnyd for potential prioritization / help in the future. Marking this as blocked for now.

[joanvr]

I'm going to collect in this comment the bits that I found during support or using the documentation that needs changes:

• Here it still mentions J.withTemplate although it no longer exists. It should be replaced with template.apply, but not sure the exact pharsing:

  rewrite-docs/concepts-and-explanations/javatemplate.md

  Line 121 in 0f262f5

  Once an instance of the template has been created it can be applied to an LST element with the method `J.withTemplate()`. This example visitor uses a template to replace all method invocations of `countLetters(String)` with `withString(String).length()`:

[mike-solomon]

As part of this - we should make sure to include information about context sensitivity. Related slack post