runtime: preserve FuncForPC names for function values

[cpunion]

Summary

• add runtime FuncForPC name lookup backed by debug symbol info
• keep command-line function-value wrappers distinct for FuncForPC so folded functions still report separate names
• cover the issue58300 pattern in test/go and remove issue58300/issue58300b goroot xfails

Tests

• go test ./test/go -run TestRuntimeFuncForPCNamesWithLLGo -count=1
• go test ./test/go -count=1
• go test ./test/goroot -count=1 -run TestGoRootRunCases -args -goroot $(go env GOROOT) -dirs fixedbugs -case '^fixedbugs/issue58300(b)?.go$' -directive-mode=ci -xfail /tmp/llgo-no-xfail.yaml -run-timeout=2m
• go test ./test/goroot -count=1 -run TestGoRootRunCases -args -goroot $(go env GOROOT) -dirs fixedbugs -case '^fixedbugs/issue58300(b)?.go$' -directive-mode=ci -run-timeout=2m
• go test ./ssa -count=1
• go test ./cl -run 'TestRunAndTestFromTestgo|TestRunAndTestFromTestrt|TestRunAndTestFromTestdata' -count=1
• git diff --check

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 81.25000% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cl/compile.go	65.00%	3 Missing and 4 partials ⚠️
ssa/interface.go	66.66%	2 Missing ⚠️

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