internal/report: fix exact function matching in disasm

[IamPritamAcharya]

Fixes #1015.

The web UI converts a selected function name into an exact regexp, for example:

^example\.com/foo\.BenchmarkWork$

disasm builds its report with address granularity. At that granularity,
NodeInfo.PrintableName() also contains the address and source location:

000000010010bfb4 example.com/foo.BenchmarkWork /tmp/foo_test.go:14

symbolsFromBinaries used the regexp against this printable name when deciding
which binary mappings to inspect. An exact function-name regexp could therefore
reject the mapping before ObjFile.Symbols had a chance to match the binary
symbol name.

Update the preliminary mapping check to also match NodeInfo.Name, which is the
function name represented by the web UI selection. Keep the existing
PrintableName() check to avoid narrowing previously supported matching
behavior. Final symbol selection continues to be performed by
ObjFile.Symbols.

The regression test exercises the web /disasm handler with an anchored
function regexp. It failed with no matches found for regexp ^F2$ before this
change. The existing unanchored disassembly case remains covered.

Validation:

• go test -v ./...
• (cd browsertests && go test)

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