FirParser grammar railroad diagram

Nobody has claimed this yet.

I've got the grammar comments in `lib/Dialect/FIRRTL/Import/FIRParser.cpp` and did some manuall fixes to be able to sse it at https://www.bottlecaps.de/rr/ui .

Copy and paste the EBNF bellow on https://www.bottlecaps.de/rr/ui tab Edit Grammar then switch to the tab View Diagram.

```
intLit ::= UnsignedInt | SignedInt | HexLit | OctalLit | BinaryLit
HexLit ::= '"' 'h' ( '+' | '-' )? ( HexDigit )+ '"'
OctalLit ::= '"' 'o' ( '+' | '-' )? ( OctalDigit )+ '"'
BinaryLit ::= '"' 'b' ( '+' | '-' )? ( BinaryDigit )+ '"'

optional-width ::= ('<' intLit '>')?

id ::= Id | keywordAsId

fieldId ::= Id | RelaxedId | UnsignedInt | keywordAsId

type ::= 'Clock'
| 'Reset'
| 'AsyncReset'
| 'UInt' optional-width
| 'SInt' optional-width
| 'Analog' optional-width
| '{' field* '}'
| type '[' intLit ']'

field::= 'flip'? fieldId ':' type

ruw ::= 'old' | 'new' | 'undefined'

exp ::= id // Ref
| prim
| integer-literal-exp
| exp '.' fieldId
| exp '[' intLit ']'
| exp '.' DoubleLit // TODO Workaround for #470
| exp '[' exp ']'
| exp '.' fieldId
| exp '[' intLit ']' | exp '[' exp ']'

prim ::= primop exp* intLit* ')'

integer-literal-exp ::= 'UInt' optional-width '(' intLit ')'
| 'SInt' optional-width '(' intLit ')'

simple_stmt_block ::= simple_stmt*

simple_stmt ::= stmt

stmt ::= attach
| memport
| printf
| skip
| stop
| when
| leading-exp-stmt
| instance
| cmem | smem | mem
| node | wire
| register

attach ::= 'attach' '(' exp+ ')' info?
stmt ::= mdir 'mport' id '=' id '[' exp ']' exp info?
mdir ::= 'infer' | 'read' | 'write' | 'rdwr'
printf ::= 'printf(' exp exp StringLit exp* ')' info?
skip ::= 'skip' info?
stop ::= 'stop(' exp exp intLit ')' info?
assert ::= 'assert(' exp exp exp StringLit ')' info?
assume ::= 'assume(' exp exp exp StringLit ')' info?
cover ::= 'cover(' exp exp exp StringLit ')' info?
when ::= 'when' exp ':' info? suite? ('else' ( when | ':' info? suite?))? suite ::= simple_stmt | INDENT simple_stmt+ DEDENT
leading-exp-stmt ::= exp '<=' exp info?
| exp '<-' exp info?
| exp 'is' 'invalid' info?
instance ::= 'inst' id 'of' id info?
cmem ::= 'cmem' id ':' type info?
smem ::= 'smem' id ':' type ruw? info?
mem ::= 'mem' id ':' info? INDENT memField* DEDENT
memField ::= 'data-type' '=>' type NEWLINE
| 'depth' '=>' intLit NEWLINE
| 'read-latency' '=>' intLit NEWLINE
| 'write-latency' '=>' intLit NEWLINE
| 'read-under-write' '=>' ruw NEWLINE
| 'reader' '=>' id+ NEWLINE
| 'writer' '=>' id+ NEWLINE
| 'readwriter' '=>' id+ NEWLINE

node ::= 'node' id '=' exp info?
wire ::= 'wire' id ':' type info?
register ::= 'reg' id ':' type exp ('with' ':' reset_block)? info?

reset_block ::= INDENT simple_reset info? NEWLINE DEDENT
| '(' simple_reset ')'
simple_reset ::= simple_reset0
| '(' simple_reset0 ')'
simple_reset0::= "reset" "=>" '(' exp exp ')'
pohwist ::= port*
port ::= dir id ':' type info? NEWLINE
dir ::= 'input' | 'output'
module ::= 'module' id ':' info? INDENT pohwist simple_stmt_block DEDENT
| 'extmodule' id ':' info? INDENT pohwist defname? parameter* DEDENT
defname ::= 'defname' '=' id NEWLINE
parameter ::= 'parameter' id '=' intLit NEWLINE
| 'parameter' id '=' StringLit NEWLINE
| 'parameter' id '=' floatingpoint NEWLINE
| 'parameter' id '=' RawString NEWLINE
file ::= circuit
circuit ::= 'circuit' id ':' info? INDENT module* DEDENT EOF

```

Start with the grammar comments in lib/Dialect/FIRRTL/Import/FIRParser.cpp and compare them with the supplied EBNF. Paste the grammar into the Bottlecap Railroad Diagram editor to check whether it renders, then determine where the resulting diagram should be recorded or published. Done means the FIRParser grammar has a usable railroad diagram and the chosen artifact location is clear.

Written by the indexing model from the issue text.