reify RHS of "value" variable
According to the [documentation](https://hackage.haskell.org/package/template-haskell-2.12.0.0/docs/Language-Haskell-TH-Syntax.html#t:Info), when reifying value variables "returning the RHS has not yet been implemented because of lack of interest". I'd like to formally request interest since I don't see a ticket here (may have missed it).
My motivating example is to make source available for documentation and better error messages. Something like:
```hs
printSource :: Name -> Q Exp
printSource n = do
VarI _ _ (Just dec) <- reify n
lift $ pprint dec
foo x = x * 2
fooSource = $(printSource 'foo) -- === "\x_0 -> x_0 GHC.Num.* 2"
```
How significant of a change is this? I could take a pass at it if pointed to the relevant bits, having not contributed to GHC before.
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 8.2.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"reify RHS of \"value\" variable","status":"New","operating_system":"","component":"Template Haskell","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.2.1","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"FeatureRequest","description":"According to the [https://hackage.haskell.org/package/template-haskell-2.12.0.0/docs/Language-Haskell-TH-Syntax.html#t:Info documentation], when reifying value variables \"returning the RHS has not yet been implemented because of lack of interest\". I'd like to formally request interest since I don't see a ticket here (may have missed it).\r\n\r\nMy motivating example is to make source available for documentation and better error messages. Something like:\r\n\r\n{{{#!hs\r\nprintSource :: Name -> Q Exp\r\nprintSource n = do\r\n VarI _ _ (Just dec) <- reify n\r\n lift $ pprint dec\r\n\r\nfoo x = x * 2\r\nfooSource = $(printSource 'foo) -- === \"\\x_0 -> x_0 GHC.Num.* 2\"\r\n}}}\r\n\r\nHow significant of a change is this? I could take a pass at it if pointed to the relevant bits, having not contributed to GHC before.","type_of_failure":"OtherFailure","blocking":[]} -->
issue