Bundle of fixes/improvements to extension

[jabraham17]

This PR bundles a number of fixes and improves to the extension

Features

• The extension is no longer reliant on a CHPL_HOME value
• Can detect and use prefix-based installs
• Added better error detection and handling
  • When CLS/chplcheck has crashed, the status bar now also has a notification to show that these are not working correctly.
• Removed the ability to build the tools automatically, this was error prone and only rarely the "correct" course of action
• Syntax highlighting for format string specifiers

List of fixes

• Resolve issues with searching PATH
• Fix syntax highlighting for numbers and the count operator

Tested locally with two versions of a chapel, a CHPL_HOME build from source and with a prefix install from homebrew

[Reviewed by @ShreyasKhandekar]

[ShreyasKhandekar]

Here's a screenshot of the status bar when the tools are not working. I think it looks nice, and that it ties with the theme being used in VS Code