[wasm] Allow user to set `-s ENVIRONMENT` setting

[radekdoulik]

The environment setting can save small amount of size in dotnet.js.

It would be nice to autodetect which environment is needed during build or at least have a way to override it.

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Issue Details

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The environment setting can save small amount of size in dotnet.js.

It would be nice to autodetect which environment is needed during build or at least have a way to override it.

Author:	radekdoulik
Assignees:	-
Labels:	arch-wasm, area-Build-mono
Milestone:	7.0.0