compile --rule-file pattern only once / extracted regular expressions code to separate file

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This is mainly so the issues are reported on start-up instead on each file. It does not improve performance much.

The refactoring and improved testing will also make it easier to add support for PCRE2 since PCRE is EOL since quite a while (see https://trac.cppcheck.net/ticket/10610).

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This needs to be a shared pointer because the it is used in Settings are they are being copied (the copies in production code will hopefully go away soon) and we have dynamic memory.

This means that multiple threads will use this but as the used data is const there should not be any issues. I did not see anything related to thread safety in the PCRE documentation. I will check again though. I hope any potential issues will be caught by the CI.

Thinking about that we a --rule test which actually has multiple input files. Wil add that.

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So it seems the shared pointers do not seem to work with forked processes.

But there is something else:

[processfs_1.cpp :0]: (error) Internal error: Child process exited with 1

I wonder where the whitespace in the filename is coming from.

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So it seems the shared pointers do not seem to work with forked processes.

The problem is that the memory behind the shared pointer is leaked in the forked process:

=================================================================
==8818==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 1248 byte(s) in 13 object(s) allocated from:
    #0 0x560b0513391f in malloc (/home/runner/work/cppcheck/cppcheck/cmake.output/bin/testrunner+0x4a791f) (BuildId: 6af36c8d50c9763d4f05b83d43e79ba4537c85c0)
    #1 0x7f7c196469b9  (/lib/x86_64-linux-gnu/libpcre.so.3+0x559b9) (BuildId: 3982f316c887e3ad9598015fa5bae8557320476a)

Indirect leak of 1056 byte(s) in 4 object(s) allocated from:
    #0 0x560b0513391f in malloc (/home/runner/work/cppcheck/cppcheck/cmake.output/bin/testrunner+0x4a791f) (BuildId: 6af36c8d50c9763d4f05b83d43e79ba4537c85c0)
    #1 0x7f7c1961f2a3  (/lib/x86_64-linux-gnu/libpcre.so.3+0x2e2a3) (BuildId: 3982f316c887e3ad9598015fa5bae8557320476a)

SUMMARY: AddressSanitizer: 2304 byte(s) leaked in 17 allocation(s).