feat: Accept function for the clear option.

[coreyfarrell]

This allows conditional removal of sourcesContent entries based on
associated filename.

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This is useful for bundles created for web pages. It can be desirable for the entry-point to be the same filename before/after bundling. So you have src/index.html importing src/index.js which imports a bunch of other sources. You copy src/index.html to build/index.html, but build/index.js is the bundle, not the source. All other files which became part of the bundle are copied to the appropriate place within build/ so browsers can find them via sourceMap.sources, but src/index.js needs to be in the source map.

Note for my own purposes a way to say "clear all sourcesContent which are not associated with sourceMap.file" would be good enough but I figured this callback would be more generic.

[phated]

This looks great. Thanks @coreyfarrell

[phated]

Published as 1.1.0