Lists of ideas for startup time improvements of small workloads identified during investigation of #120288:

• Expensive dictionary in socket error map (fixed by Use switch statement to map socket errors #120364)
• Remove redundant Guid parsing in RuntimeEventSource's static constructor (fixed by Remove redundant guid parsing #120413)
• Expensive GUID lookup/generation in EventSource initialization (Avoid custom attribute routine in NetEventSource #120422 and Add EventSource guid ctors for non-reflection creation #28290)
• R2R rejected for methods implemented using SIMD (Vector128.CopyTo discards R2R #120367)
• Load ICU more lazily (Don't trigger ICU loading in string.ToUpperInvariant #120685)
• R2R code missing for static interface methods (R2R code missing for static interface methods #120405)
• 1000 more types loaded in .NET 10 vs. .NET 8 (1000 more types loaded in .NET 10 vs. .NET 8 during startup in a small workload #120406)
• Resolution of static virtual methods in the JIT interface is O((N + M)*C) where N is the number of MethodImpl records on a type, M is the number of MethodImpl records on all interfaces which are implemented on a type, and C is the number of calls in the method being jitted.
• Missing profile data for libcoreclr.so on Linux (the profile data seems to have methods for libclrjit.so only)
• Startup regression for the first 25 invocations Startup regression in milli-core containers for the first 25 invocations #120681
• R2R for Vector64/128/256/512 instantiations R2R contains unnecessary compilations for certain generic types #120816
• ASP.NET shared framework is missing PGO data
• Merge debugger and diagnose server threads into one
• Eliminate Win32 PAL thread (part of Eliminate Windows PAL layer for non-Windows CoreCLR builds #31721)