[HLE] Stub ContentExport, Font, and Pad calls Astro Bot needs to boot (#298)

Astro Bot asserts and null-writes when a subsystem init call fails, so
each missing import surfaces as a named crash. This stubs the blockers
observed during bring-up: content export init, eight font calls, and
pad tilt correction. sceFontGetHorizontalLayout writes the same
invented geometry as sceFontGetRenderCharGlyphMetrics and the rest
report success. Together with save data memory2 these take the title
to its splash image and font glyph rendering path.

tests/SharpEmu.Libs.Tests/Font/FontExportsTests.cs

@@ -0,0 +1,44 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Buffers.Binary;
+using SharpEmu.HLE;
+using SharpEmu.Libs.Font;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.Font;
+
+public sealed class FontExportsTests
+{
+    private const ulong Base = 0x1_0000_0000;
+    private const ulong LayoutAddress = Base + 0x100;
+
+    private readonly FakeCpuMemory _memory = new(Base, 0x1000);
+    private readonly CpuContext _ctx;
+
+    public FontExportsTests()
+    {
+        _ctx = new CpuContext(_memory, Generation.Gen5);
+    }
+
+    // SceFontHorizontalLayout is three floats; the sentinel directly after
+    // them must survive the call.
+    [Fact]
+    public void GetHorizontalLayout_WritesExactlyThreeFloats()
+    {
+        const uint Sentinel = 0xDEADBEEF;
+        Span<byte> sentinelBytes = stackalloc byte[sizeof(uint)];
+        BinaryPrimitives.WriteUInt32LittleEndian(sentinelBytes, Sentinel);
+        Assert.True(_ctx.Memory.TryWrite(LayoutAddress + 12, sentinelBytes));
+
+        _ctx[CpuRegister.Rsi] = LayoutAddress;
+        Assert.Equal(0, FontExports.GetHorizontalLayout(_ctx));
+
+        Span<byte> layout = stackalloc byte[16];
+        Assert.True(_ctx.Memory.TryRead(LayoutAddress, layout));
+        Assert.Equal(12.0f, BinaryPrimitives.ReadSingleLittleEndian(layout));
+        Assert.Equal(16.0f, BinaryPrimitives.ReadSingleLittleEndian(layout[4..]));
+        Assert.Equal(0.0f, BinaryPrimitives.ReadSingleLittleEndian(layout[8..]));
+        Assert.Equal(Sentinel, BinaryPrimitives.ReadUInt32LittleEndian(layout[12..]));
+    }
+}