Fix: Use fallback if RoutePattern is MVC.

[lucas-zimerman]

Despite a context feature having a RouteEndpoint, it doesn't mean we can use the RawText value of the RoutePattern since it may result in a default route for different paths.
For a simple fix, I opted to just use the fallback to get the MVC route since we didn't have any proper data of the Route Template on the given Endpoint.

Additionally, that the SDK is creating transactions for items like loading a CSS file, thus results in Unknown Routes. If desired, we could use context.Request.Path.Value as a last fallback for cases like that.

Sample:

Also, the issue can be easily reproduced on the sample Sentry.Samples.AspNetCore.Mvc

Close #1189.

[codecov-commenter]

Codecov Report

Merging #1188 (8142f71) into main (c307373) will decrease coverage by 0.04%.
The diff coverage is 58.33%.

❗ Current head 8142f71 differs from pull request most recent head fdc1b71. Consider uploading reports for the commit fdc1b71 to get more accurate results

@@            Coverage Diff             @@
##             main    #1188      +/-   ##
==========================================
- Coverage   80.55%   80.51%   -0.05%     
==========================================
  Files         212      212              
  Lines        6891     6902      +11     
  Branches     1573     1579       +6     
==========================================
+ Hits         5551     5557       +6     
  Misses        822      822              
- Partials      518      523       +5     

Impacted Files	Coverage Δ
...try.AspNetCore/Extensions/HttpContextExtensions.cs	82.75% <58.33%> (-17.25%)	⬇️

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