* Promote ChiselEnum user APIs from experimental (#2929)

They are commonly used and if we were ever to change them, we will need
to go through a deprecation process anyway.

Note that the EnumAnnotations remain in chisel3.experimental because,
like all Chisel annotation support, they are slated to be deprecated and
removed.

(cherry picked from commit 424e9446f1675fe0168e22bdfbbe85db997376e6)

# Conflicts:
#	docs/src/cookbooks/verilog-vs-chisel.md
#	docs/src/explanations/chisel-enum.md

* Maintain binary compatbility, use aliases in chisel3 package

* Deprecate the actual classes in chisel3.experimental
* Also fix backport conflicts

Co-authored-by: Jack Koenig <koenig@sifive.com>

* Add internal methods to maintain binary compatibility

Co-authored-by: Megan Wachs <megan@sifive.com>
Co-authored-by: Jack Koenig <koenig@sifive.com>

* Cleanup Cookbook and printing docs
* Format specifiers are actually concise now

Co-authored-by: Megan Wachs <megan@sifive.com>
(cherry picked from commit df2a71833ffc8ee8a053a1e8ea41c482e46be132)

Co-authored-by: Aditya Naik <91489422+adkian-sifive@users.noreply.github.com>

(cherry picked from commit 1ad820f7f549eddcd7188b737f59a240e48a7f0a)

Co-authored-by: Zachary Yedidia <zyedidia@gmail.com>

(cherry picked from commit 0b2c211beefeefb72c86ea69a0b2a0101b2f2c20)

Co-authored-by: Megan Wachs <megan@sifive.com>

(cherry picked from commit 81fcf229da84e334cdc466ffbb8ea74c7975a4a9)

Co-authored-by: Megan Wachs <megan@sifive.com>

Links between markdown pages should not have any file extension to ensure they work on the website.

(cherry picked from commit 04d4dc6da11678d0f12f84913fc05359d9a998a1)

Co-authored-by: Jack Koenig <koenig@sifive.com>

* Define leading '_' as API for creating temporaries

Chisel and FIRRTL have long used signals with names beginning with an
underscore as an API to specify that the name does not really matter.
Tools like Verilator follow a similar convention and exclude signals
with underscore names from waveform dumps by default. With the
introduction of compiler-plugin prefixing in Chisel 3.4, the convention
remained but was hard for users to use unless the unnnamed signal
existed outside of any prefix domain. Notably, unnamed signals are most
useful when creating wires inside of utility methods which almost always
results in the signal ending up with a prefix.

With this commit, Chisel explicitly recognizes signals whos val names
start with an underscore and preserve that underscore regardless of any
prefixing. Chisel will also ignore such underscores when generating
prefixes based on the temporary signal, preventing accidental double
underscores in the names of signals that are prefixed by the temporary.

(cherry picked from commit bd94366290886f3489d58f88b9768c7c11fa2cb6)

* Remove unused defaultPrefix argument from _computeName

(cherry picked from commit ec178aa20a830df2c8c756b9e569709a59073554)

# Conflicts:
#	core/src/main/scala/chisel3/Module.scala
#	core/src/main/scala/chisel3/experimental/hierarchy/ModuleClone.scala

* Resolve backport conflicts

* Waive false positive binary compatibility errors

Co-authored-by: Jack Koenig <koenig@sifive.com>

(cherry picked from commit 98fdfc5e609099cb4fb1749132cc62236148c6da)

Co-authored-by: Megan Wachs <megan@sifive.com>