Fix Activity http.route and name

[alanwest]

Fixes #3485
Fixes #3461
Fixes #2967
Fixes #3771

This PR fixes a number of items with respect to the Activity.DisplayName and http.route attribute:

• Activity.DisplayName now conforms to the specification
  • It is set to {http.method} {http.route} when there is a low-cardinality http.route
  • It is {http.method} when there is not a low-cardinality http.route
• http.route was missing for some attribute-based routing scenarios
• http.route was missing when using minimal API
• http.route, when present, is now the same for both the Activity and metric emitted

There remain scenarios not fixed by this PR and also changes their behavior. You can review this readme for the scenarios that remain unresolved. In summary:

• When using conventional-based routing, http.route is set to the matched route template. This does not accurately reflect the actual route when the controller/action invoked are not the defaults. For example:
  • See this test case.
    • The path invoked is /ConventionalRoute/ActionWithStringParameter/2?num=3
    • http.route is set to {controller=ConventionalRoute}/{action=Default}/{id?}
    • Ideally, http.route would be something like ConventionalRoute/ActionWithStringParameter/{id?}.
• When using Razor pages and invoking the root path (e.g. http://example.com/), http.route is empty.
  • See this test case
    • The path invoked is '/'
    • http.route attribute is not set
    • Ideally, http.route would be /Index because that is the default page.

These scenarios are unfortunate because it limits users from meaningfully querying metrics and faceting them by http.route. See open-telemetry/opentelemetry-dotnet-contrib#1730 and open-telemetry/opentelemetry-dotnet-contrib#1729.

[codecov]

Codecov Report

Merging #5026 (dbb9e37) into main (2a228f9) will increase coverage by 0.08%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    open-telemetry/opentelemetry-dotnet#5026      +/-   ##
==========================================
+ Coverage   83.61%   83.69%   +0.08%     
==========================================
  Files         296      296              
  Lines       12484    12483       -1     
==========================================
+ Hits        10438    10448      +10     
+ Misses       2046     2035      -11     

Flag	Coverage Δ
unittests	83.69% <100.00%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...umentation.AspNetCore/AspNetCoreInstrumentation.cs	100.00% <ø> (ø)
...tation.AspNetCore/Implementation/HttpInListener.cs	91.57% <100.00%> (-0.30%)	⬇️
...AspNetCore/Implementation/HttpInMetricsListener.cs	89.23% <100.00%> (-0.17%)	⬇️
src/Shared/RequestMethodHelper.cs	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

[vishweshbankwar]

Tagging few other issues: #3485 #2967 #3771

[vishweshbankwar]

Proposed changes looks good to me.

[alanwest]

Opened these issues to highlight the remaining known issues related to http.route.

@JamesNK I'm interested in your thoughts. I'm hoping we can coordinate to resolve these issues.