[JENKINS-60866][JENKINS-71513] Adapt to upcoming st:bind change

[daniel-beck]

Related to jenkinsci/stapler#385 and jenkinsci/jenkins#6865.

This is not strictly required, as Stapler/Jenkins will continue to work as before even with the existing code, but this PR demonstrates the change in behavior (without this change, it's the backward compatibility mode, with this change it's the new behavior).

Currently this tag emits something like the following when running on the core PR build:

<script>window.bindings['buildMonitor']=makeStaplerProxy('/jenkins/$stapler/bound/<UUID>','<CSRF_CRUMB>',['fetchJobViews']);</script>

With this change, on the Jenkins PR build, it's instead

<script src="/jenkins/$stapler/bound/script/jenkins/$stapler/bound/<UUID>?var=buildMonitorBind&amp;methods=fetchJobViews" type="application/javascript"></script>

(Behavior changes based on whether var is a legal identifier or not, and it's not without the PR.)

This does not result in the rest of this plugin (or even this file) becoming compatible with https://plugins.jenkins.io/csp/ or whatever form that'll take in Jenkins core in the future, but that's beyond the scope of this PR.

Testing done

Opened a BM view and the Stapler proxy calls happened periodically, both with and without this change, when running the core PR incremental build.

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[basil]

Shouldn't there be a semicolon at the end of this statement?

[daniel-beck]

Probably safer to have it, not strictly necessary though.