Feature: add extensionsToIgnore to withExtensions

[namzug16]

Description

extensionsToIgnore has been added to withExtensions which allows developers to filter the extensions within the internal api.

Corresponding issue:
bigskysoftware/htmx-extensions#145

Testing

Please explain how you tested this change manually, and, if applicable, what new tests you added. If
you're making a change to just the website, you can omit this section.

I've manually tested it by creating an extension merge-vals that modifies the parameters through encodeParameters, while being used at the same time with json-enc-custom like so

...
hx-ext="merge-vals,json-enc-custom"
...

the extension implementation:

    encodeParameters: function(xhr, parameters, elt) {
      xhr.overrideMimeType("text/json");

      let mergedVals = api.mergeObjects({}, parameters);

      if (elt.hasAttribute("hx-merge-vals")) {
        ...
        // simplified code
      }

      return JSON.stringify(mergedVals);
    }

The issue with this implementation is that htmx will only use the first extension that modifies the parameters, so json-custom-enc will never be used

a simple fix would to manually call the extensions like so

    encodeParameters: function(xhr, parameters, elt) {
      xhr.overrideMimeType("text/json");

      let mergedVals = api.mergeObjects({}, parameters);

     ...
     // simplified code
     
      api.withExtensions(elt, function(extension) {
        mergedVals = JSON.parse(extension.encodeParameters(xhr, mergedVals, elt))
      })

      return JSON.stringify(mergedVals);
    }

Now, a different issue arises, withExtensions will get all the specified extensions from the element, including merge-vals which will cause an infinity loop

This PR introduces extensionsToIgnore into withExntensions which fixes this issue without the introduction of a breaking change to the logic of encode parameters

    encodeParameters: function(xhr, parameters, elt) {
      xhr.overrideMimeType("text/json");

      let mergedVals = api.mergeObjects({}, parameters);

     ...
     // simplified code
     
      api.withExtensions(elt, function(extension) {
        mergedVals = JSON.parse(extension.encodeParameters(xhr, mergedVals, elt))
      }, ["merge-vals"])

      return JSON.stringify(mergedVals);
    }

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