new version scheme

[chuckadams]

Right now we're declaring ourselves to be a beta of 6.7, but we should have our own versioning in place that's independent of what version of WordPress it claims to be compatible with.

$wp_version is global and used all over the place in core and very likely in plugins, so it's probably going to have to remain 6.7 or whatever upstream version we claim compatibility with. For the separate yet-unnamed project version variable, I'm inclined to go either with the scheme used by Ubuntu, e.g. 24.10 or with the JetBrains versioning of YYYY.n where n increases for each release that year (usually 4), e.g. 2024.1. Currently leaning toward the latter, since the minor version won't have "gaps" in the numbering and allows more than one release a month (however unlikely that is).

Currently $wp_version = '6.7-beta1-59152-src and is unchanging. This gets bumped by the copy:version task in the Gruntfile, but it also relies on SVN to get a build number for pre-release versions. Putting the git commit hash in a "build id" isn't bad, but it won't sort for versions