Build: Version comes from git tag, ChangeLog, Jamulus.pro

> My concern is `get_build_version()` uses a different value. The tag, `Jamulus.pro` and `ChangeLog` could all have different versions.

> Given we have three sources for the version, we really need automation to make sure they're aligned, at least: i.e. error out if things look wrong. But I agree, that's not in scope here. For that, it sounds like (and I don't fully understand how this works):
> * If the tag is set, we should use that to determine build type and version and that source should overrule others.
> * ChangeLog and Jamulus.pro "target" versions should match - and, if set, match the tag build type and version.
> * If the tag wasn't set, build type and version can then come from ChangeLog and Jamulus.pro, as needed.

_Originally posted by @pljones in https://github.com/jamulussoftware/jamulus/pull/2656#discussion_r901061485_

Start by tracing get_build_version() and comparing its behavior with the version declarations in Jamulus.pro and ChangeLog. Inspect how git tags determine build type and version. Done means the version sources are aligned or mismatches are detected, including the tag and no-tag cases described in the issue.

Written by the indexing model from the issue text.