Make invalidFmtError public and use in place of compileErrors for bad format strings

[nickcernis]

• Renames invalidFmtErr() to invalidFmtError() (for consistency; Zig seems to use Error more than Err).
• Makes invalidFmtError public, as suggested by @Vexu in Improve Version format compile error #13489.
• Uses invalidFmtError in place of @compileError when bailing due to bad format strings.

Goals are to:

• Reduce use of custom strings to give more consistent format errors.
• Give users info about the type of the value they formatted incorrectly to help them find and fix it.
• Make invalidFmtError the standard way of reporting bad format strings in Zig and for users.

Example

const std = @import("std");
const builtin = @import("builtin");
const Guid = std.os.uefi.Guid;

pub fn main() !void {
    std.debug.print("{s}", .{builtin.zig_version});

    const guid = Guid{
        .time_low = 0x09576e91,
        .time_mid = 0x6d3f,
        .time_high_and_version = 0x11d2,
        .clock_seq_high_and_reserved = 0x8e,
        .clock_seq_low = 0x39,
        .node = [_]u8{ 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b },
    };

    std.debug.print("{badformat}", .{guid});
}

Error before	Error after
Unknown format string: 's'	invalid format string 's' for type 'SemanticVersion'
Unknown format character: 'badformat'	invalid format string 'badformat' for type 'os.uefi.Guid'

[Vexu]

Thanks! This is nice improvement to make using custom formatters more consistent. I went ahead and added these checks to the remaining custom formatters in std.