(GH-306) Add a syntax aware code folding provider

[glennsarti]

Fixes #306

Previously the Puppet Lexer ignored whitespace and comments and did not generate any token information. This meant it could not be used for code formatting purposes. This commit adds a new lexer which sub-classes the original and emits tokens for comments. Later commits can use this lexer for operations like code folding and as-you-type formatting.

This commit also memoizes the tokens in the document store so documents do not need to be lexed multiple times for the same version.

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Previously the Language Server dod not provide code folding hints, and the client was left to use its defauly, typically indentation based. This commit:

• Adds a manifest folding provider, which can extract code folding regions based on block comments, multiline comments and blocks of code ( { -> } and [ -> ] )
• Adds many tests to ensure that regions are detected correctly particuarly in nested situations, or within HEREDOC strings.

• Note that this folding is only supported on Puppet 6.3.0 and above due to the needed features in the Puppet Langauge tokeniser

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Now that there is a Puppet Manifest Folding provider available, the server capabilities need to be updated so that clients know to use it. This commit:

• Creates a method on ServerCapabilities to determine if folding is supported by the server
• Updates the Service Capabilities to advertise the 'foldingRangeProvider' capavility if it is supported but not dynamic registrations
• Updates the Client Settings to send dynamic registrations 'textDocument/foldingRange' if supported
• Adds a two new settings for Folding: Enabled and Show Last Line
• Refactors the Language Client settings to make it easier to set defaults
• Updated Server to respond to 'textDocument/foldingRange' requests

Adds many tests for the message handler and language client for the new provider

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Task list

• [x] Add tests for document store that it ejects tokens when a different document version is used

[glennsarti]

Before	After

[glennsarti]

This adds two new settings

puppet.editorService.foldingRange.enable : Turns on or off the syntax folding provider. Supports dynamic registration (No restart required). Defaults to True

puppet.editorService.foldingRange.showLastLine : Whether to show the last line in the folding range. Some people like the whole range hidden. Some people want to see the trailing line. Defaults to True which is the VSCode default

[glennsarti]

Requires Puppet 6.3.0 or above to work due to the needed Lexer methods. Silently disables if it encounters it.

This also sets up the work to move off of the puppet-lint lexer for the hash rock alignment.

[glennsarti]

@jpogran Ready for review.

[jpogran]