[vcpkg] Add mingw dynamic libs triplet

[longnguyen2004]

Describe the pull request

• What does your PR fix? Fixes #
  This PR adds 4 triplets for building dynamic libs with mingw toolchain, and rename the old static libs triplets to *-static, following the *-windows triplets convention
  Currently, building with this triplet will fail, due to the post-build validation only checking for .lib files, not .dll.a files, but the building process seems to be ok, at least for CMake-based libs. So we only have that left to fix. Added VCPKG_POLICY_DLLS_WITHOUT_LIBS as a workaround.

• Which triplets are supported/not supported? Have you updated the CI baseline?
  Should be all *-mingw triplets, but I've only tested x64-mingw

• Does your PR follow the maintainer guide?
  Yes

[LilyWangL]

/azp run

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[LilyWangL]

/azp run

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[vicroms]

The only concern I have is that this PR changes the behavior of already existing triplets for MinGW, and will break users that have already adopted those triplets.

[vicroms]

I think a good compromise is to rename both triplets: <arch>-mingw-static and <arch>-mingw-dynamic.

[longnguyen2004]

So *-mingw would be the same as *-mingw-static, got it

[vicroms]

I say we remove <arch>-mingw, and force users to use the explicit <arch>mingw-static and <arch>mingw-dynamic triplets. That way existing users will get an error for deprecated behavior instead of changing the library linkage without them noticing.

[ras0219-msft]

Thanks for the PR!