Rename BigDecimal to decimal in Swift5

[dammafra]

According to PR #7808 this line should be fixed.

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/Swift5ClientCodegen.java

Line 220 in 7392499

typeMapping.put("BigDecimal", "Decimal");

[wing328]

@dammafra thanks for pointing it out. I've filed #7875 to fix it.

[teameh]

#7875 has been merged, this issue can be closed @wing328