Maintenance mode

- Use regular expressions to get version strings more rigorously
- Add version discriminant function, you can compare version size
- Correct the version comparison of antlr under special conditions
- Improve the version comparison of protoc

Signed-off-by: Huang Rui <vowstar@gmail.com>

Transformation of mem readwriters whose address contain references to
readwriters of mems declared before it would contain invalid references
to untransformed memory readwriter, as the connection is not transformed.
This commit fixes this issue.

This will make it easier to compile circuits with
older compiler versions.

* [smem] fix read-under-write serialization

Also adds some tests for the parser and
the serializer.

* Serializer: always serialize smem ruw behavior

* test: simplify smem test circuit

Based on https://github.com/chipsalliance/chisel3/pull/2901.

* allow for zero-width integer literals
* CheckWidths: ensure that width is non-negative

* Enhance find_heap_bound to not go smaller than min_step

Previously, it could accidentally get a step size smaller than the
min_step and just continue looping forever. Now the while loop has a new
termination condition to catch this case.

* Add context to find_heap_bound

This new option allows for checking additional heap sizes in increments
of the min_step above the found minimum heap size.

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* Update protobuf-java to 3.18.3

* Revert commit(s) 4b5cbaf1

* Update protobuf-java to 3.18.3

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Also get rid of whitespace-only lines that were emitted after every when
block.

This is needed for emitting modules that serialize to Strings larger
than 2 GiB (the maximum String size on the JVM). It includes
micro-optimized logic for turning arbitrarily nested when scopes into
Iterable[String].

Ever since introducing the Listener, the firrtl Parser now can hit
errors in the code converting from concrete syntax to abstract syntax
that may be due to syntax errors. These errors are essentially broken
assumptions about the structure of the parsed code because there is an
error. These errors are reported before the standard ANTLR syntax errors
are aggregated and reported, and thus could result in less than elegant
error messages (eg. NullPointerException). Now, the Parser will mask off
such errors in the event of standard syntax errors caught by the
ANTLR-generated parser.

This commit also cleans up some ParserSpec tests slightly to make the
ScalaTest style more canonical.

* Parse version and hardcode emitted version

* Throw error if version is too high

* Parse version even if rest is invalid

* Change pattern match to if statement

* Improve version grammar

* Update tests

* Remove outdated comment

* Simplify grammar and use version class

* Simplify and add no version test

* Fix for conflicting lexer rule

The simple functionality is needed in chiseltest.

* Fix Yosys link
* Update SBT version

Fixes #2516

Previously,

reg r : UInt<8>, clock with :
  reset => (p, UInt<8>(3))
r is invalid

would compile to:

reg r : UInt<8>, clock
r <= UInt<8>(0)

now it compiles to:

reg r : UInt<8>, clock
wire r_1 : UInt<8>
r_1 is invalid
r <= mux(reset, UInt<8>(3), r_1)

This is consistent with the behavior for a reset with an asynchronous
reset.

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