Add CLI version switching

[jribbink]

Closes #538

Description

Adds ability to select versions of the CLI with native support for flow-c1

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[jribbink]

tests pass locally - there are seemingly issues with @vscode/test-electron that break these, will be addressed subsequently (probably need to update)

[bthaile]

lgtm

[bthaile]

How does the correct language server get chosen based on the version of flow-cli used?

[jribbink]

How does the correct language server get chosen based on the version of flow-cli used?

The LanguageServerAPI watches for the binary to change from the CliProvider and will restart accordingly. I realized it maybe wasn't super clear, so I've moved some stuff around and added some more comments to make it more obvious that this is how it works.