Use mapping file provider in case of legacy Variant API

[0xnm]

What does this PR do?

This PR makes to use Variant.mappingFileProvider in case of legacy API usage. This brings more reliable way to get a mapping file.

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• [ ] Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.09677% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 78.16%. Comparing base (70ba81c) to head (03f0863). Report is 3 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #265 +/- ## ============================================= - Coverage 78.25% 78.16% -0.10% - Complexity 249 250 +1 ============================================= Files 31 31 Lines 892 911 +19 Branches 114 114 ============================================= + Hits 698 712 +14 - Misses 144 147 +3 - Partials 50 52 +2 ``` | [Files](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog) | Coverage Δ | | |---|---|---| | [...com/datadog/gradle/plugin/DdAndroidGradlePlugin.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?src=pr&el=tree&filepath=dd-sdk-android-gradle-plugin%2Fsrc%2Fmain%2Fkotlin%2Fcom%2Fdatadog%2Fgradle%2Fplugin%2FDdAndroidGradlePlugin.kt&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9EZEFuZHJvaWRHcmFkbGVQbHVnaW4ua3Q=) | `71.34% <100.00%> (+1.09%)` | :arrow_up: | | [...atadog/gradle/plugin/internal/CurrentAgpVersion.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?src=pr&el=tree&filepath=dd-sdk-android-gradle-plugin%2Fsrc%2Fmain%2Fkotlin%2Fcom%2Fdatadog%2Fgradle%2Fplugin%2Finternal%2FCurrentAgpVersion.kt&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC9DdXJyZW50QWdwVmVyc2lvbi5rdA==) | `50.00% <100.00%> (+16.67%)` | :arrow_up: | | [...tadog/gradle/plugin/internal/variant/AppVariant.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?src=pr&el=tree&filepath=dd-sdk-android-gradle-plugin%2Fsrc%2Fmain%2Fkotlin%2Fcom%2Fdatadog%2Fgradle%2Fplugin%2Finternal%2Fvariant%2FAppVariant.kt&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC92YXJpYW50L0FwcFZhcmlhbnQua3Q=) | `0.00% <ø> (ø)` | | | [...gradle/plugin/internal/variant/NewApiAppVariant.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?src=pr&el=tree&filepath=dd-sdk-android-gradle-plugin%2Fsrc%2Fmain%2Fkotlin%2Fcom%2Fdatadog%2Fgradle%2Fplugin%2Finternal%2Fvariant%2FNewApiAppVariant.kt&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC92YXJpYW50L05ld0FwaUFwcFZhcmlhbnQua3Q=) | `56.67% <ø> (-3.33%)` | :arrow_down: | | [...dle/plugin/internal/variant/LegacyApiAppVariant.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265?src=pr&el=tree&filepath=dd-sdk-android-gradle-plugin%2Fsrc%2Fmain%2Fkotlin%2Fcom%2Fdatadog%2Fgradle%2Fplugin%2Finternal%2Fvariant%2FLegacyApiAppVariant.kt&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC92YXJpYW50L0xlZ2FjeUFwaUFwcFZhcmlhbnQua3Q=) | `60.71% <77.78%> (+4.62%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/265/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog)