Constrain aspire-starter port replacers to localhost: URLs (#20031)

The dynamic port symbols (webHttpPortReplacer, apiServiceHttpPortReplacer,
appHostHttpPortReplacer, etc.) used a bare numeric "replaces" value, so the
template engine substituted that number everywhere in generated content, not
just in launchSettings.json. Since the default ports (5000, 7000, 5301, 7301,
15000, 17000, 19000, 20000, 21000, 22000) also occur as plain numeric literals
in vendored files such as wwwroot/lib/bootstrap/dist/js/bootstrap.bundle.js
(e.g. carousel interval: 5000), those files ended up with churned values that
differ between generated projects, making diffs across template runs noisy.

Add "onlyIf": [{"after": "localhost:"}] to each port replacer so substitution
only fires in "localhost:<port>" contexts, matching the fix already applied
upstream for the same class of bug (dotnet/aspnetcore#65165, dotnet/sdk#48811).

Fixes #20030