Meson: extract config vars defined inside configuration_data({...})

[masatake]

I should pull this request into two.

( This random should be removed from here:

input : "\n" L3781
match :'\n'            main[ 0] / ^([a-zA-Z_][a-zA-Z_0-9]*)[ \t\n]*=([^=]|$)/
match :'\n'            main[ 1] / ^project[ \t\n]*\\([ \t\n]*'([^']*[^\\\\])'[ \t\n]*/
match :'\n'            main[ 2] / ^subdir[ \t\n]*\\([ \t\n]*'([^']*[^\\\\])'[ \t\n]*/
match :'\n'            main[ 3] / ^test[ \t\n]*\\([ \t\n]*'([^']*[^\\\\])'[ \t\n]*/
match :'\n'            main[ 4] / ^[ \t\n]+/

...                   TABLE[ N] ...
result: matched 1 bytes
scope : 
action: NOP in {main}, stack: /

It would be helpful for optimization if ctags could report per-TABLE statistics (average N, s.d. N, max N). )

[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 65 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 85.87%. Comparing base (d80d5de) to head (8511130). :warning: Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
optlib/meson.c	0.00%	65 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4275      +/-   ##
==========================================
- Coverage   85.94%   85.87%   -0.08%     
==========================================
  Files         248      248              
  Lines       63539    63593      +54     
==========================================
  Hits        54608    54608              
- Misses       8931     8985      +54     

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[masatake]

Surprisingly, per-table statistics were already implemented: --totals=extra.