[context][fix] Use the property instead of the field for analyzer env

[Szelethus]

AnalyzerContext.__analyzer_env is lazy initialized via AnalyzerContext.analyzer_env. __parse_CC_ANALYZER_BIN became the first to use it, but erronously accessed the field directly -- which wasn't initialized at that time.

[dkrupp]

Looks like it works fine based on my tests

So if CC_ANALYZERS_FROM_PATH is unset
the lookup order is
CC_ANALYZER_BIN then
package_layout.json then PATH

if CC_ANALYZERS_FROM_PATH is set
the lookup order is
CC_ANALYZER_BIN then PATH

Could you please describe this in https://github.com/Ericsson/codechecker/blob/master/docs/analyzer/user_guide.md#configuring-clang-version ?

Could you please add a few Test cases?
given:

unset CC_ANALYZERS_FROM_PATH
echo $CC_ANALYZER_BIN
gcc:/usr/bin/gcc-13

{
  "runtime": {
    "analyzers": {
      "clangsa": "/usr/bin/clang",
      "clang-tidy": "/usr/bin/clang-tidy",
      "cppcheck": "cppcheck",
      "gcc": "g++"
    },
    "clang-apply-replacements": "clang-apply-replacements"
  },
  "ld_lib_path_extra" : [],
  "path_env_extra" : []
}```

clangsa should be taken from /usr/bin/clang, the package config
gcc: gcc:/usr/bin/gcc-13 (from CC_ANALYZER_BIN)

2)

CC_ANALYZERS_FROM_PATH=1
echo $CC_ANALYZER_BIN 
gcc:/usr/bin/gcc-13
PATH=/opt/llvm/bin:$PATH

clangsa should be taken from the PATH: /opt/lllvm/bin
gcc:/usr/bin/gcc-13  (configured from CC_ANALYZER_BIN)

[Szelethus]

I agree, but that is a separate issue worthy of a separate PR.

[dkrupp]

LGTM provided that you write a test case for this.