Ports: Add abseil and protobuf

Abseil's Serenity support is a little limited:
- No support for any timezone shenanigans since protobuf hopefully
  doesn't use those. For now, abseil will always believe to be in UTC on
  Serenity.
- In most places where explicit platforms need to be added to a list of
  supported platforms, Serenity will be missing. Again I only added the
  ones that are required for protobuf.

Ports/abseil/package.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port='abseil'
+useconfigure='true'
+version='20230802.0'
+configopts=(
+    "-DCMAKE_TOOLCHAIN_FILE=${SERENITY_BUILD_DIR}/CMakeToolchain.txt"
+    '-DABSL_PROPAGATE_CXX_STD=ON'
+    '-DABSL_ENABLE_INSTALL=ON'
+    '-DABSL_BUILD_TESTING=OFF'
+)
+files=(
+    "git+https://github.com/abseil/abseil-cpp.git#${version}"
+)
+
+configure() {
+    run cmake . "${configopts[@]}"
+}
+
+build() {
+    run cmake --build .
+}
+
+install() {
+    run cmake --build . --target install
+}