Dangerous `const` to `var` rollup plugin

[lforst]

#5917 revealed something we didn't fully consider when writing our const to var rollup plugin. This plugin is supposed to reduce bundle size but it also has a semantic impact that can lead to opaque bugs.

We should definitely reconsider if we want to keep this plugin, or if we should at least change it to a "const to let" plugin.

Plugin in question:

sentry-javascript/rollup/plugins/npmPlugins.js

Line 37 in 56868e8

export function makeConstToVarPlugin() {