refactor(fs): eliminate srcShared/ namespace

[justinmk3]

Problem

The srcShared/ concept is not necessary, and confusing to explain. Instead, a more tractable and less-churn approach is:

1. Assume that ALL modules are "cross platform" (i.e. they support both nodejs and web-mode).
2. Web-only logic lives in a fooWeb.ts module or a web/ directory relative to its namespace.
3. Nodejs-only logic lives in a fooNodejs.ts module or a nodejs/ directory relative to its namespace.

See also:

• https://github.com/aws/aws-toolkit-vscode/pull/5046#discussion_r1614541013
• https://github.com/aws/aws-toolkit-vscode/pull/5248#discussion_r1661084971

Solution

• Move fs.ts into shared/.
• Delete srcShared/.

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[justinmk3]

/runintegrationtests