Do not execute hx-trigger="load" on re-initialization of an existing node

[basvk]

Description

Sometimes, requests that should be only triggered once at load (with hx-trigger="load") are executed twice. This happens for example when calling htmx.process on an existing node (or a parent node) after changing an attribute on the element with hx-trigger="load". This PR adds a firstInitCompleted flag to an element's internalData and adds a check for that flag when handling the load triggerEvent.

Corresponding issue:

2973

Testing

Added a test scenario that changes hx-swap="afterbegin" to hx-swap="beforeend" on an element with hx-trigger="load", followed by a call to htmx.process and checks whether the innerHTML of the element stayed the same. This test fails on the dev branch, and passes with this fix.

Checklist

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

[basvk]

Thanks, good idea! I've changed firstInit into firstInitCompleted and removed that unnecessary check in initNode.