Add CMD_HELP UDTF for fast CL command hover documentation

[bobcozzi]

Summary

This PR adds a fast primary path for CL command hover documentation using a SQL Table Function (CMD_HELP) that wraps the IBM i QUHRHLPT API. The existing GENCMDDOC-based path is preserved as a fallback.

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Problem

Hovering over a CL command or parameter currently calls GENCMDDOC, which:

• Requires the Db2 for i JVM to be warm (cold-start adds 15–30 seconds)
• Generates a full HTML document and writes it to the IFS
• Downloads the file over a second SSH round-trip
• Runs through the ileQueue, serializing behind any active compile

Even with a warm JVM, GENCMDDOC typically takes 5–15 seconds, making the hover feature impractical for everyday use. Many users disable it entirely via general.displayCommandDocumentation.

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Solution

A new CmdHelpChecker IBMiComponent installs a C++ service program (CMDHELP) and SQL Table Function (CMD_HELP) into the connection's tempLibrary on first connect. The UDTF wraps QUHRHLPT directly and returns HTML help text for a specific parameter keyword or the entire command — all via a single SQL call.

Signature:

CMD_HELP(library VARCHAR(10), cmd VARCHAR(10), helpid VARCHAR(6000))
RETURNS TABLE (HELP_XML CLOB(16M))

Pass the command name as helpid for command-level help, or a parameter keyword (e.g. MSGID) for parameter-level help. Despite the column name, the returned content is HTML.

The hover provider now:

1. Calls CMD_HELP first — returns in under a second, no JVM required
2. Converts the returned HTML to Markdown using NodeHtmlMarkdown
3. Falls back to the existing GENCMDDOC path if CMD_HELP is unavailable or returns no data

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Files Changed

File	Change
client/src/components/cmdHelp/cmdHelpChecker.ts	New IBMiComponent — auto-installs/updates the UDTF on connect
client/src/components/cmdHelp/cmdHelpCppSource.ts	Embedded base64-encoded C++ source for CMDHELP service program
client/src/components/cmdHelp/cmdHelpSqlSource.ts	SQL DDL that creates/replaces the CMD_HELP UDTF
client/src/gencmddoc.ts	New getCLDocParam() method — queries CMD_HELP and returns Markdown
client/src/extension.ts	Registers CmdHelpChecker; adds getCLDocParam LSP request handler
server/src/instance.ts	New getCLDocParam() LSP request helper
server/src/providers/hover.ts	CMD_HELP fast path with GENCMDDOC fallback
client/src/components/syntaxChecker/checker.ts	Minor: DBGVIEW(*LIST) → DBGVIEW(*NONE)

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Behaviour

• If CMD_HELP is installed and returns data → hover shows immediately with a "View Full Documentation" link that triggers GENCMDDOC on demand
• If CMD_HELP is not yet installed, or SQL runner unavailable → silently falls back to existing GENCMDDOC path (no regression)
• The C++ source is base64-encoded in the TypeScript file to avoid false-positive antivirus flags in the VS Code Marketplace
• CmdHelpChecker uses the standard IBMiComponent version mechanism — if the UDTF source changes in a future release, getRemoteState() will detect the stale version and update() will recompile automatically

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Testing

Tested with Code for IBM i on IBM i 7.5. Hover response time dropped from 8–12 seconds (GENCMDDOC cold) to under 1 second (CMD_HELP).

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Contributed by @BobCozzi

[bobcozzi]

I saw PR70 after I created this, so I applied the same async pattern to CmdHelpChecker.
I would also suggest that you change the DBVIEW(*LIST) parameter to DBGVIEW(*NONE) so the C++ can be optimized--there's no use for a debug listing in this functions. If there is need to debug, the end-user can recompile with that option (the code is over on my github page anyway).