log/slog: export Source method in Record for custom handler support

[nesty92]

Currently, the source method in slog.Record is not accessible to
custom handlers, requiring developers to re-implement logic for
retrieving source location information. This commit exports the source
method as Source, enabling consistent access for custom logging
handlers and reducing code redundancy.

Fixes #70280

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Patch Set 1:

(1 comment)

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Patch Set 1:

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Message from Ernesto Alejandro Santana:

Patch Set 1:

(1 comment)

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Patch Set 2: Hold+1

(1 comment)

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