Unify method/action resolution and improve hx-action doco

[MichaelWest22]

Description

Found we can improve hx-action to fall back to formmethod and method native attributes just like hx-boost already does. This allows some better progressive enhancement options when moving to use the more natural action based attribute. You can place a hx-action on a form and have it use native method attributes.

By combining hx-action and hx-boost action and method calculation logic it also simplifies the code required as well.

Updated doco to highlight the progressive enhancment options and method fallback.

Corresponding issue:

Testing

Added new hx-action tests to cover the new behavior. should be no problem breaking changes for valid existing use cases as we are just adding a method fallback that was not usable before and it would have been confusing before if native method did not override the method used.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded