Fix version build number in DEB and RPM package info

[sharon-wang]

Summary

• addresses Positron Build Number is 0 in DEB and RPM package version info #5159
• related to positron CLI returns VS Code version #1373
• a follow-up to Update positron cli and linux package info with positron version output #5072 to fix up the DEB and RPM package info build number

Changes

• The positronBuildNumber from the package.json file will always be zero -- instead, we need to use the calculated build number from show-version.js when possible.
• We are already using the calculated build number in a few places, but a few were missing, resulting in a build number of zero 0 in the DEB and RPM package info.
• The positronBuildVersion variable is now in a separate util file, so the value can be used across the gulpfiles.

QA Notes

I've checked the version output of the DEB on Ubuntu 24 (x86_64) and the RPM on Fedora 40 (arm).

DEB

1. Run dpkg --info <POSITRON_BINARY>.deb
2. Confirm the Version field in the output shows <POSITRON_VERSION>+<BUILD_NUMBER>-<LINUX_REVISION>

Sample Output:

<SOME_INITIAL_INFO>
Package: positron
Version: 2024.11.0+999-1729709839
<REST_OF_INFO>

RPM

1. Run rpm -qi <POSITRON_BINARY>.rpm
2. Confirm the Version field in the output shows <POSITRON_VERSION>+<BUILD_NUMBER>

Sample Output:

Name        : positron
Version     : 2024.11.0+999
<REST_OF_INFO>