Mono: Allow specifying fixed git hash and pretty image version

Specifying only a branch like '2019-08' is problematic if upstream commits
something between the builds of two containers.

We could make a tarball in the first container build and reuse that, but we
need the flexibility of Git for some patching in the Android and JavaScript
builds, so instead we allow specifying a git tree-ish as the third argument.

We can therefore also give a pretty version string to use for the image name
as second argument, e.g. 6.6.0.160 for bef1e6335812d32f8eab648c0228fc624b9f8357.

As we can't `git clone` a commit hash directly, we still need to provide both
branch name and then commit hash for this use case.

Dockerfile.windows

@@ -2,6 +2,7 @@ ARG img_version
 FROM godot-mono:${img_version}
 
 ARG mono_version
+ARG mono_commit
 
 RUN if [ -z "${mono_version}" ]; then echo -e "\n\nargument mono-version is mandatory!\n\n"; exit 1; fi && \
     dnf -y install --setopt=install_weak_deps=False \
@@ -9,7 +10,9 @@ RUN if [ -z "${mono_version}" ]; then echo -e "\n\nargument mono-version is mand
     dnf clean all
 
 RUN git clone https://github.com/mono/mono --branch ${mono_version} --single-branch && \
-    cd mono && git submodule update --init && \
+    cd /root/mono && \
+    if [ ! -z "${mono_commit}" ]; then git checkout ${mono_commit}; fi && \
+    git submodule update --init && \
     NOCONFIGURE=1 ./autogen.sh && \
     ./configure --prefix=/root/dependencies/mono-64 --host=x86_64-w64-mingw32 --disable-boehm --disable-mcs-build --disable-executables && \
     echo '#define HAVE_STRUCT_SOCKADDR_IN6 1' >> config.h && \
@@ -27,7 +30,7 @@ RUN git clone https://github.com/mono/mono --branch ${mono_version} --single-bra
     echo '#define HAVE_STRUCT_SOCKADDR_IN6 1' >> config.h && \
     make -j && \
     make install && \
-    cd .. && \
+    cd /root && \
     cp /root/dependencies/mono-32/bin/libMonoPosixHelper.dll /root/dependencies/mono-32/bin/MonoPosixHelper.dll && \
     rm -f /root/dependencies/mono-32/bin/mono /root/dependencies/mono-32/bin/mono-sgen && \
     ln -s /usr/bin/mono /root/dependencies/mono-32/bin/mono && \