feat(tracemetrics): Convert equation alias to full equation for queries

[narsaynorath]

The RPC endpoint for tracemetrics doesn't take equation[0] as a valid sort and expects the full equation|... format. This PR ensures that when we make requests to the datasets with sorts (e.g. grouped series, or categorical bar charts) that the full equation is used.

This is done by updating two surfaces:

• Updating the series query params to treat DiscoverDatasets.TRACEMETRICS similar to spans and logs, which use RPC and have the same constraints/handling
• Update the table request for categorical bar charts to detect if the sort is an equation alias, then get the index, get the equations, and use the right equation index to set the sort
• Remove equation handling for the widget builder table sort because all datasets that support equations now support the full equation format. It's only the case that some datasets (RPC datasets) don't support the alias format

This shouldn't require feature-flagging because it's gated on having the equation builder, which itself is feature flagged.

I did a bunch of this PR manually and guided with claude before I realized there was a lot simpler of an implementation where we can internally use the equation[0] syntax for now and convert on the requests. At that point I prompted it to remove a bunch of the old cruft, rework the stuff that remained, and add tests.

[github-actions]

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[DominikB2014]

lgtm! just small nit to use a utility function for dealing with sorts