fix(engine): fix color contrast issues for text with image/gradient background or shadow

[shunguoy]

• Rule bug: IBMA_Color_Contrast_WCAG2AA IBMA_Color_Contrast_WCAG2AA_PV

This PR is related to the following issue(s):

#1201 #1202 #1203 #1205

Additional information can be found here:

Testing reference:

note that this branch was merged with the branch dev-1304 in PR #1432. The test should be done using the branch dev-1304 and with the following test cases.

1. test/v2/checker/accessibility/rules/IBMA_Color_Contrast_WCAG2AA_ruleunit/act_pass_4.html (now is reported as a potential violation, rather than violation). test/v2/checker/accessibility/rules/IBMA_Color_Contrast_WCAG2AA_ruleunit/act_pass_7.html, test/v2/checker/accessibility/rules/IBMA_Color_Contrast_WCAG2AA_ruleunit/special-chars-1.html
2. test/v2/checker/accessibility/rules/IBMA_Color_Contrast_WCAG2AA_ruleunit/*.html. please note the rule IBMA_Color_Contrast_WCAG2AA_PV was merged to IBMA_Color_Contrast_WCAG2AA, make sure all the issues, previously reported in the two rules, are still reported.
3. the major fix is to eliminate the exceptions during the build (the exceptions don't cause build errors).

I have conducted the following for this PR:

• [ x] I validated this code in Chrome and FF
• [x ] I validated this fix in my local env
• [x ] I provided details for testing
• This PR has been reviewed and is ready for test
• [ x] I understand that the title of this PR will be used for the next release notes.

[ErickRenteria]

1. Tested with equal-access/accessibility-checker-engine/test/v2/checker/accessibility/rules/Rpt_Aria_RequiredParent_Native_Host_Sematics_ruleunit/ACT_ff89c9_pass4.html No changes. @shunguoy

[shunguoy]

@ErickRenteria looks like you got the wrong test case: Tested with equal-access/accessibility-checker-engine/test/v2/checker/accessibility/rules/Rpt_Aria_RequiredParent_Native_Host_Sematics_ruleunit/ACT_ff89c9_pass4.html.
Please see the "Testing Reference" section for the correct test cases. Note that the "IBMA_Color_Contrast_WCAG2AA" was renamed to "ext_contrast_sufficient" so the file paths need to be renamed accordingly.

[ErickRenteria]

Validated with accessibility-checker-engine/test/v2/checker/accessibility/rules/text_contrast_sufficient_ruleunit/act_pass_7.html