[FIRRTL] Generic intrinsic parsing/emitter support

[dtzSiFive]

Add parsing and emitter support for FIRRTL intrinsic.

Refactor parameter parsing on (ext/int)modules as these use same syntax.

Snippet from parse-basic.fir without FileCheck directives:

circuit GenericIntrinsics:
  public module GenericIntrinsics:
    input clock : Clock
    input data : UInt<32>
    input c : UInt<1>

    ; Statements
    intrinsic(circt_verif_assert, c)
    intrinsic(circt_fpga_probe, data, clock)

    ; Expressions
    node n = intrinsic(circt_plusargs_value<FORMAT = "foo"> : { found : UInt<1>, result : UInt<5> })
    node n2 = intrinsic(circt_plusargs_test<FORMAT = "bar"> : UInt<3>)

    ; Statement with unused return value.
    intrinsic(circt_clock_gate : Clock, clock, c)

    ; Nesting, statement and expression forms.
    intrinsic(circt_verif_assert, intrinsic(circt_isX: UInt<1>, data))

And somewhat similarly from the emit-basic test:

  public module GenericIntrinsic :
    input clk : Clock
    input c : UInt<1>
    output s : UInt<32>
    output io1 : UInt<1>
    output io2 : UInt<1>
    output io3 : UInt<1>
    output io4 : UInt<5>

    connect s, intrinsic(circt_sizeof : UInt<32>, clk)
    connect io1, intrinsic(circt_isX : UInt<1>, clk)
    connect io2, intrinsic(circt_plusargs_test<FORMAT = "foo"> : UInt<1>)
    intrinsic(circt_clock_gate : Clock, clk, c)
    node _gen_int
      = intrinsic(circt_plusargs_value<FORMAT = "foo">
                    : { found : UInt<1>, result : UInt<5> })
    connect io3, _gen_int.found
    connect io4, _gen_int.result
    intrinsic(circt_verif_assert, intrinsic(circt_isX : UInt<1>, c))
    node _gen_int_0 = intrinsic(circt_isX : UInt<1>, c)
    intrinsic(circt_verif_assert, intrinsic(circt_isX : UInt<1>, _gen_int_0))

[fabianschuiki]

Nice refactoring of the parameter parsing! Looks good to me. Gonna let others comment on the syntax.

[mikeurbach]

I took a quick look through it, and the implementation looks good to me. I'm happy to approve as-is, not sure if anyone else wants to weigh in or have a deeper design review. To me, the fact that the parsing logic is relatively straightforward and not going through crazy gyrations means the syntax is effective.

[dtzSiFive]

Added commit moving to the left-paren keyword specifically so that this is safe w.r.t. backwards-compatibility with designs that parse today as it only changes what happens when someone writes intrinsic( which is never legal presently.

[uenoku]

LGTM

[dtzSiFive]

Landing, thanks for the reviews/feedback all!

Syntax is not official, but let's keep this train moving and modify as needed 👍