[Instrumentation.AspNet] Improved route template normalization performance

[matt-hensley]

Changes

Reworked route template normalization from #3160 to improve CPU and memory usage.

Thanks for sharing the benchmark code @RassK!

BenchmarkDotNet v0.15.4, Windows 11 (10.0.26100.6584/24H2/2024Update/HudsonValley)
AMD Ryzen 5 PRO 6650U with Radeon Graphics 2.90GHz, 1 CPU, 12 logical and 6 physical cores
  [Host]     : .NET Framework 4.8.1 (4.8.9310.0), X86 LegacyJIT
  DefaultJob : .NET Framework 4.8.1 (4.8.9310.0), X86 LegacyJIT


| Method                      | Mean     | Error     | StdDev    | Ratio | RatioSD | Gen0       | Allocated | Alloc Ratio |
|---------------------------- |---------:|----------:|----------:|------:|--------:|-----------:|----------:|------------:|
| PrepareRouteTemplate_String | 3.077 ms | 0.0166 ms | 0.0147 ms |  1.00 |    0.01 |  2539.0625 |   2.33 MB |        1.00 |
| PrepareRouteTemplate_Alt    | 1.413 ms | 0.0054 ms | 0.0050 ms |  0.46 |    0.00 |  1541.0156 |   1.41 MB |        0.61 |

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.15%. Comparing base (3a5b8ee) to head (1d083c7).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3241      +/-   ##
==========================================
+ Coverage   69.92%   70.15%   +0.22%     
==========================================
  Files         440      430      -10     
  Lines       16974    16935      -39     
==========================================
+ Hits        11869    11880      +11     
+ Misses       5105     5055      -50     

Flag	Coverage Δ
unittests-Instrumentation.AspNet	77.92% <100.00%> (+0.68%)	⬆️
unittests-Instrumentation.Cassandra	?

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

Files with missing lines	Coverage Δ
...on.AspNet/Implementation/HttpRequestRouteHelper.cs	100.00% <100.00%> (ø)

... and 15 files with indirect coverage changes

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[Kielek]

LGTM.

Potential follow up: Do you see any place when we can even more drop memory allocation by some Spans?