use cobra command for llcppg

[tsingbx]

llcppg has too many features
the new llcppg, the llcppgx, purely user-oriented.

The usage of the llcppgx command is simplified as follows:

1. llcppgx init libcjson Initializes libcjson
2. llcppgx gensym Generates and edits the symbol table
3. llcppgx genpkg -mod "github.com/goplus/cjson" Generates a Go package

The number of command-line flags is reduced.

[codecov]

Codecov Report

❌ Patch coverage is 4.06091% with 189 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.44%. Comparing base (7955d98) to head (e847864).

Files with missing lines	Patch %	Lines
cmd/internal/base/base.go	0.00%	44 Missing ⚠️
cmd/internal/genpkg/genpkg.go	0.00%	38 Missing ⚠️
config/parse.go	18.18%	35 Missing and 1 partial ⚠️
cmd/internal/gencfg/gencfg.go	0.00%	28 Missing ⚠️
config/config.go	0.00%	15 Missing ⚠️
cmd/internal/gencfg/flags.go	0.00%	7 Missing ⚠️
cmd/internal/gensig/gensig.go	0.00%	5 Missing ⚠️
cmd/internal/gensym/gensym.go	0.00%	5 Missing ⚠️
cmd/internal/version/version.go	0.00%	4 Missing ⚠️
cmd/internal/genpkg/flags.go	0.00%	3 Missing ⚠️
... and 2 more

❗ There is a different number of reports uploaded between BASE (7955d98) and HEAD (e847864). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (7955d98)	HEAD (e847864)
	3	2

Additional details and impacted files

@@ Coverage Diff @@## main #582 +/- ##
==========================================
- Coverage 84.19% 78.44% -5.76% 
==========================================
Files 27 38 +11 Lines 2746 2500 -246 ==========================================
- Hits 2312 1961 -351 - Misses 391 496 +105 
Partials 43 43 

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