Improve optics processor

[nomisRev]

Closes #848

[nomisRev]

@arrow-kt/maintainers After discussion with @JorgeCastilloPrz I updated this PR to generated code as follows:

1. The file must be generated with the same package as the annotated target (Generate classes on target class packages #765)
2. Folder structure must match the target's package.
3. The file name must match annotated target name + some postfix.

i.e.

package com.domain.my

@optics data class Person(val name: String, val age: Int)

Result should be in a file kaptKotlin/main/com/domain/my/Person$$optics.kt

If everyone agrees should we write this down somewhere in a Contributor wiki? (I thought we had one, did we remove it?)

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d7c1931). Click here to learn what that means.
The diff coverage is 53.88%.

@@            Coverage Diff            @@
##             master     #852   +/-   ##
=========================================
  Coverage          ?   44.65%           
  Complexity        ?      615           
=========================================
  Files             ?      303           
  Lines             ?     7771           
  Branches          ?      837           
=========================================
  Hits              ?     3470           
  Misses            ?     4000           
  Partials          ?      301

Impacted Files	Coverage Δ	Complexity Δ
...essor/src/main/java/arrow/optics/AnnotationInfo.kt	100% <ø> (ø)	0 <0> (?)
.../src/main/java/arrow/optics/PrismsFileGenerator.kt	100% <ø> (ø)	0 <0> (?)
.../src/main/java/arrow/optics/DslSnippetGenerator.kt	0% <0%> (ø)	0 <0> (?)
...ssor/src/main/java/arrow/optics/OpticsProcessor.kt	58.73% <57.14%> (ø)	31 <16> (?)
...ssor/src/main/java/arrow/optics/AnnotatedDomain.kt	78.12% <76.66%> (ø)	0 <0> (?)
...or/src/main/java/arrow/optics/IsosFileGenerator.kt	78.26% <80%> (ø)	0 <0> (?)
.../src/main/java/arrow/optics/LensesFileGenerator.kt	94.44% <94.44%> (ø)	0 <0> (?)
...rc/main/java/arrow/optics/OptionalFileGenerator.kt	95% <94.44%> (ø)	0 <0> (?)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d7c1931...0847863. Read the comment docs.

[raulraja]

👍