every `EmitOption` field in `std.Build.Step.Compile` (for example: `emit_docs`) lacks `FileSource` integration

[andrewrk]

zig/lib/std/Build/Step/Compile.zig

Lines 49 to 58 in b9fc0d2

	emit_analysis: EmitOption = .default,
	emit_asm: EmitOption = .default,
	emit_bin: EmitOption = .default,
	emit_docs: EmitOption = .default,
	emit_implib: EmitOption = .default,
	emit_llvm_bc: EmitOption = .default,
	emit_llvm_ir: EmitOption = .default,
	// Lots of things depend on emit_h having a consistent path,
	// so it is not an EmitOption for now.
	emit_h: bool = false,

Instead of passing strings directly to the Zig CLI, the build system API should have a function for adding emission of each of these artifacts which returns a FileSource which can then be used as inputs in other parts of the build system API.

As an example, getOutputSource already does this for the CLI equivalent of -femit-bin.

As a bonus, the build system should pass -fno-emit-bin unless getOutputSource() is called on the Compile Step. This will happen automatically in the case of adding an install step for the build artifact, which passes the result of getOutputSource() to an Install Step.

[ikskuh]

I'll try resolving this with a PR together with #16353