Deno support for LSP and fixer

[motato1]

Deno is a JavaScript and TypeScript runtime akin to Node, however it does not use Node packages/npm.
As of version 1.6.0, Deno brings its own Language Server implementation, though it is not yet feature-complete (see denoland/deno#8643).

This PR integrates Deno LSP support as well as the built-in fixer (deno fmt) into ALE (TypeScript only).

Currently, no version check is performed to see if LSP is supported (although I mention the required version in the help file).
If that is a requirement, please let me know. Also, a pointer to an example of how version checks are usually performed in ALE would be helpful.

[hsanson]

ALE migrated from Travis to Github Actions (see #3548) so it is necessary to rebase this PR from latest master branch to trigger the required checks.

# Add dense-analysis as remote upstream on your local fork. Not 
# needed if already added.
git remote add upstream https://github.com/dense-analysis/ale.git

# Sync your local master with upstream master
git checkout master
git fetch upstream master
git merge upstream/master

# Rebase the PR branch with master
git checkout my-branch-name
git rebase master   # Fix any conflicts you may have

# Force push the updated PR branch to origin to trigger the checks
git push -f origin my-branch-name

[motato1]

Thank you.
I rebased my branch onto upstream master and fixed the documentation to satisfy the linters.

[hsanson]

Looks good, thanks.