…#13398)

#### What this PR does

This PR adds support for the `anchored` and `smoothed` range selector
modifiers into the Mimir query engine.

ie `eval instant at 60s metric[1m] anchored` or `eval instant at 60s
metric[1m] smoothed`

This is the equivalent implementation to
[prometheus/pull/16457](prometheus/prometheus#16457
) and the original proposal for this extension can be [found
here](prometheus/proposals#52).

A new CLI argument has been added to enable these extensions;

```-query-frontend.enabled-promql-extended-range-selectors=smoothed,anchored```

The `experimental_functions.go` middleware has been extended (and renamed) to also manage the tenant access to use these extensions. As part of adding support for this, the error messages when a function/aggregate/modifier is not enabled has been updated to correctly identify if the denied keyword is a function, aggregate or extended range modifier.

#### Which issue(s) this PR fixes or relates to

Fixes #3260

#### Checklist

- [ x] Tests updated.
- [ ] Documentation added.
- [x ] `CHANGELOG.md` updated - the order of entries should be `[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry is not needed, please add the `changelog-not-needed` label to the PR.
- [x ] [`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md) updated with experimental features.



Notes to reviewers;

* there is a prometheus PR which will need to be merged and vendored into mimir - prometheus/prometheus#17479. This is not a blocker, but once merged will enable full use of upstream test files.

The other note is to call attention the oddity in the use of `smoothed` ranges in rate/increase functions.

Prometheus calculates the range boundary values differently when the range is used in one of these functions. In the prometheus implementation, the entire matrix is re-walked to do these different calculations. See https://github.com/prometheus/prometheus/blob/main/promql/functions.go#L128-L173

To avoid this, you will see that I pre-calculate these alternate values on the range boundary and pass these along with the step data. These are interpolated calculations and it would seem more efficient to pre-calculate these and not use them rather then to have to later re-walk the data. 

I also did not attempt to determine if the parent of the range vector was a rate/increase function and use this to decide which boundary point calculation to use. The reason for this was in case this range vector result was ever cached / re-used then this implementation may be confusing.  


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds MQE support for experimental `smoothed` and `anchored` range selector modifiers with per-tenant enablement, updated planning/execution, and docs/flags.
> 
> - **MQE/Execution**:
>   - Implement extended range selector modifiers `smoothed` and `anchored` in range and instant selectors, including extended-boundary handling and smoothed basis points for rate/increase.
>   - Update rate/increase/delta logic to honor modifiers; disallow with native histograms; validate modifier-function compatibility.
>   - Enable parser extended-range selectors in frontend/querier; clone `Anchored`/`Smoothed` in AST.
> - **Planning/Protocol**:
>   - Propagate modifier flags through planning (core proto), raise minimum plan version to `V4`.
>   - Add planner errors for unsupported functions with these modifiers.
> - **Middleware/Gating**:
>   - Replace experimental functions middleware with unified experimental features middleware to gate functions, aggregations, and extended range modifiers; improve error messages per feature type.
> - **Config/CLI/Docs**:
>   - Add `-query-frontend.enabled-promql-extended-range-selectors` (per-tenant) with defaults, help text, config descriptor, and operations defaults.
>   - Update docs (`about-versioning`, configuration parameters) and CHANGELOG entries.
> - **Tests/Benchmarks**:
>   - Add extensive unit/plan tests, testdata, and benchmark cases for new modifiers.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 49b1131. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Taylor C <41653732+tacole02@users.noreply.github.com>
Co-authored-by: Charles Korn <charles.korn@grafana.com>
Co-authored-by: Charles Korn <charleskorn@users.noreply.github.com>
Co-authored-by: Nick Pillitteri <56quarters@users.noreply.github.com>