Improve SymbolProvider.ts

[msftrncs]

Overhaul of SymbolProvider.ts to more thoroughly process well known POU symbols excluding symbol discovery in comments or quoted text, and with recovery of parsing on syntax errors where ever possible.

• This adds POU detection of INTERFACE, METHOD, ACTION keywords.
• This adds symbol discovery for VAR_GLOBAL and others.
• This adds symbol discovery for all VAR's even when not nested in appropriate POU's.
• This prevents symbols being inappropriately detected in commented areas or quoted strings.
• This adds symbol discovery for comma separated variable definitions.
• This corrects discovery of symbols following the attribute keywords, such as RETAIN, CONSTANT, PERSISTENT, PUBLIC, PRIVATE, etc...
• This adds symbol discovery for multiple instances of the same VAR keyword, often utilizing different attributes.
• This adds detection of CONSTANT symbols.
• This adds discovery of non STRUCT based types (simple types).
• This adds discovery of symbols in UNION structures.
• This improves, for all symbols, the navigation and breadcrumb features in VS Code, by providing the full document positions for the symbol.
• This attempts to stop discovery of symbols with common keywords, which may occur during normal editing, cutting and pasting, etc...
• This may have altered the original vscode.SymbolKind selections for some symbols.
• This may have dropped some description elements for some symbols.
• This may still need some refinement on symbol description for complex symbol definitions, ex (POINTER TO ARRAY[x..y] OF FB_ProcessSomething.
• This PR should be considered a work in progress until it has been communicated (from either side) otherwise. (and this line removed)

References issue #25.

[msftrncs]

I've tested and it works fine. Although it works very slow. Anyway, could you please resubmit this PR against develop branch? I use Git Flow, so master is the latest release.

It might be slower for sure, but on my system with most the files I have used it with, including the test.st file, it populates the outline nearly instantly. The regex's are fairly complicated, and have to consume large amounts of the document carefully in order to insure they only find valid closing keywords/punctuation. As a reference, the VS Code TextMate grammar.ts file takes about 3 seconds to provide symbols for a 1500 line file. The test.st file loads symbols so fast it appears instantly for me, at 1000 lines. My machine is a 8th gen Core i7.

[Serhioromano]

Perfect! I'll make another review and release new version today.

[msftrncs]

I'm (was) going to force one more commit, cleaned some unneeded sections from regex to not skip over quoted strings where an identifier is expected.

I'll commit it up to the same branch. You can take a look at it at your leisure, as its really minor.