Limit character set according to spec

[mic-max]

Changes

\w matches to more than just the intended a-zA-Z0-9_ https://learn.microsoft.com/en-us/dotnet/standard/base-types/character-classes-in-regular-expressions#word-character-w

Before the change the addition to InvalidInstrumentNames would fail the test. the value is aµ. The Micro is considered Letter, Lowercase by the \w match. But this is just to show that any character belonging to the categories shown could have made an instrument name become out of spec.

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #3821 (18239e8) into main (f921ae3) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3821      +/-   ##
==========================================
+ Coverage   87.46%   87.48%   +0.01%     
==========================================
  Files         280      280              
  Lines       10767    10767              
==========================================
+ Hits         9417     9419       +2     
+ Misses       1350     1348       -2     

Impacted Files	Coverage Δ
...lemetry/Metrics/Builder/MeterProviderBuilderSdk.cs	92.85% <100.00%> (ø)
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...tpListener/Internal/PrometheusCollectionManager.cs	73.62% <0.00%> (-2.20%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	96.21% <0.00%> (+1.08%)	⬆️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	82.35% <0.00%> (+2.94%)	⬆️
...lementation/SqlClientInstrumentationEventSource.cs	75.00% <0.00%> (+4.16%)	⬆️
...Propagators/OpenTelemetryPropagatorsEventSource.cs	100.00% <0.00%> (+12.50%)	⬆️