Modify Webpack sourcemap parameters to account for Windows path separators.

[Varriount]

The basics

• I validated my changes

The details

Proposed Changes

This PR modifies the Webpack configurations throughout the repository such that:

• The regular expression used to determine which sourcemaps to load/look for works on Windows systems.
• The regular expression used to determine which sourcemap parsing errors to ignore only covers paths containing the term "blockly"

Reason for Changes

Prior to this change, Blockly source maps wouldn't load on Windows systems, as Windows uses a backslash as a path separator, not a forward slash. The parsing error regex was modified as it occurred to me that it was overly broad, and might hide meaningful errors over the course of regular development.

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