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/protobuf/package.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port='protobuf'
+useconfigure='true'
+version='24.3'
+depends=(
+    'abseil'
+    'zlib'
+)
+configopts=(
+    "-DCMAKE_TOOLCHAIN_FILE=${SERENITY_BUILD_DIR}/CMakeToolchain.txt"
+    '-Dprotobuf_BUILD_TESTS=OFF'
+    # Don't use Protobuf's internal abseil, which is missing from the archive anyways.
+    '-Dprotobuf_ABSL_PROVIDER=package'
+)
+files=(
+    "git+https://github.com/protocolbuffers/protobuf.git#v${version}"
+)
+
+configure() {
+    run cmake -B build -G Ninja . "${configopts[@]}"
+}
+
+build() {
+    run cmake --build build
+}
+
+install() {
+    run cmake --install build
+}