docs(dotnet): stable Metrics APIs (#16932)

## DESCRIBE YOUR PR
With the next release of the Sentry .NET SDK - expected to be `v6.3.0` -
the Metrics APIs are no longer `Experimental`.
This changeset updates the respective C# code snippets.

Related PRs:
- getsentry/sentry-dotnet#5023
- getsentry/sentry#110636

## IS YOUR CHANGE URGENT?  

Help us prioritize incoming PRs by letting us know when the change needs
to go live.
- [ ] Urgent deadline (GA date, etc.): <!-- ENTER DATE HERE -->
- [x] Other deadline: Release of the Sentry .NET SDK v6.3.0
- [ ] None: Not urgent, can wait up to 1 week+

## SLA

- Teamwork makes the dream work, so please add a reviewer to your PRs.
- Please give the docs team up to 1 week to review your PR unless you've
added an urgent due date to it.
Thanks in advance for your help!

## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [x] Checked Vercel preview for correctness, including links
- [x] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
  - [x] @jamescrosswell
- [x] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

## EXTRA RESOURCES

- [Sentry Docs contributor guide](https://docs.sentry.io/contributing/)

Co-authored-by: James Crosswell <jamescrosswell@users.noreply.github.com>

Author: 2 people

platform-includes/metrics/options/dotnet.mdx

@@ -1,6 +1,6 @@
 #### EnableMetrics
 
-Set to `false` in order to disable the `SentrySdk.Experimental.Metrics` APIs.
+Set to `false` in order to disable the `SentrySdk.Metrics` APIs.
 
 #### SetBeforeSendMetric
 
@@ -10,7 +10,7 @@ To filter metrics, or update them before they are sent to Sentry, you can use th
 SentrySdk.Init(options =>
 {
     options.Dsn = "___PUBLIC_DSN___";
-    options.Experimental.SetBeforeSendMetric(static metric =>
+    options.SetBeforeSendMetric(static metric =>
     {
         if (metric.Name == "removed-metric")
         {

platform-includes/metrics/usage/dotnet.mdx

@@ -1,4 +1,4 @@
-Metrics are enabled by default. Once you initialize the SDK, you can send metrics using the `SentrySdk.Experimental.Metrics` APIs.
+Metrics are enabled by default. Once you initialize the SDK, you can send metrics using the `SentrySdk.Metrics` APIs.
 
 The `SentryMetricEmitter` type exposes three method groups that you can use to capture different types of metric information: `Counter`, `Gauge`, and `Distribution`.
 
@@ -13,7 +13,7 @@ To emit a counter, do the following:
 
 ```csharp
 // Record five total button clicks
-SentrySdk.Experimental.Metrics.EmitCounter("button_click", 5,
+SentrySdk.Metrics.EmitCounter("button_click", 5,
     [new KeyValuePair<string, object>("browser", "Firefox"), new KeyValuePair<string, object>("app_version", "1.0.0")]);
 ```
 
@@ -25,7 +25,7 @@ To emit a distribution, do the following:
 
 ```csharp
 // Add '15.0' to a distribution used for tracking the loading times per page.
-SentrySdk.Experimental.Metrics.EmitDistribution("page_load", 15.0, MeasurementUnit.Duration.Millisecond,
+SentrySdk.Metrics.EmitDistribution("page_load", 15.0, MeasurementUnit.Duration.Millisecond,
     [new KeyValuePair<string, object>("page", "/home")]);
 ```
 
@@ -37,6 +37,6 @@ To emit a gauge, do the following:
 
 ```csharp
 // Add '15.0' to a gauge used for tracking the loading times for a page.
-SentrySdk.Experimental.Metrics.EmitGauge("page_load", 15.0, MeasurementUnit.Duration.Millisecond,
+SentrySdk.Metrics.EmitGauge("page_load", 15.0, MeasurementUnit.Duration.Millisecond,
     [new KeyValuePair<string, object>("page", "/home")]);
 ```