This MR addresses #22404.  There is a big Note

   Note [Occurrence analysis for join points]

that explains it all.  Significant changes

* New field occ_join_points in OccEnv

* The NonRec case of occAnalBind splits into two cases:
  one for existing join points (which does the special magic for
  Note [Occurrence analysis for join points], and one for other
  bindings.

* mkOneOcc adds in info from occ_join_points.

* All "bring into scope" activity is centralised in the
  new function `addInScope`.

* I made a local data type LocalOcc for use inside the occurrence analyser
  It is like OccInfo, but lacks IAmDead and IAmALoopBreaker, which in turn
  makes computationns over it simpler and more efficient.

* I found quite a bit of allocation in GHC.Core.Rules.getRules
  so I optimised it a bit.

More minor changes

* I found I was using (Maybe Arity) a lot, so I defined a new data
  type JoinPointHood and used it everwhere.  This touches a lot of
  non-occ-anal files, but it makes everything more perspicuous.

* Renamed data constructor WithUsageDetails to WUD, and
  WithTailUsageDetails to WTUD

This also fixes #21128, on the way.

--------- Compiler perf -----------
I spent quite a time on performance tuning, so even though it
does more than before, the occurrence analyser runs slightly faster
on average.  Here are the compile-time allocation changes over 0.5%

      CoOpt_Read(normal) ghc/alloc    766,025,520    754,561,992  -1.5%
CoOpt_Singletons(normal) ghc/alloc    759,436,840    762,925,512  +0.5%
     LargeRecord(normal) ghc/alloc  1,814,482,440  1,799,530,456  -0.8%
       PmSeriesT(normal) ghc/alloc     68,159,272     67,519,720  -0.9%
          T10858(normal) ghc/alloc    120,805,224    118,746,968  -1.7%
          T11374(normal) ghc/alloc    164,901,104    164,070,624  -0.5%
          T11545(normal) ghc/alloc     79,851,808     78,964,704  -1.1%
          T12150(optasm) ghc/alloc     73,903,664     71,237,544  -3.6% GOOD
          T12227(normal) ghc/alloc    333,663,200    331,625,864  -0.6%
          T12234(optasm) ghc/alloc     52,583,224     52,340,344  -0.5%
          T12425(optasm) ghc/alloc     81,943,216     81,566,720  -0.5%
          T13056(optasm) ghc/alloc    294,517,928    289,642,512  -1.7%
      T13253-spj(normal) ghc/alloc    118,271,264     59,859,040 -49.4% GOOD
          T15164(normal) ghc/alloc  1,102,630,352  1,091,841,296  -1.0%
          T15304(normal) ghc/alloc  1,196,084,000  1,166,733,000  -2.5%
          T15630(normal) ghc/alloc    148,729,632    147,261,064  -1.0%
          T15703(normal) ghc/alloc    379,366,664    377,600,008  -0.5%
          T16875(normal) ghc/alloc     32,907,120     32,670,976  -0.7%
          T17516(normal) ghc/alloc  1,658,001,888  1,627,863,848  -1.8%
          T17836(normal) ghc/alloc    395,329,400    393,080,248  -0.6%
          T18140(normal) ghc/alloc     71,968,824     73,243,040  +1.8%
          T18223(normal) ghc/alloc    456,852,568    453,059,088  -0.8%
          T18282(normal) ghc/alloc    129,105,576    131,397,064  +1.8%
          T18304(normal) ghc/alloc     71,311,712     70,722,720  -0.8%
         T18698a(normal) ghc/alloc    208,795,112    210,102,904  +0.6%
         T18698b(normal) ghc/alloc    230,320,736    232,697,976  +1.0%  BAD
          T19695(normal) ghc/alloc  1,483,648,128  1,504,702,976  +1.4%
          T20049(normal) ghc/alloc     85,612,024     85,114,376  -0.6%
         T21839c(normal) ghc/alloc    415,080,992    410,906,216  -1.0% GOOD
           T4801(normal) ghc/alloc    247,590,920    250,726,272  +1.3%
           T6048(optasm) ghc/alloc     95,699,416     95,080,680  -0.6%
            T783(normal) ghc/alloc    335,323,384    332,988,120  -0.7%
           T9233(normal) ghc/alloc    709,641,224    685,947,008  -3.3% GOOD
           T9630(normal) ghc/alloc    965,635,712    948,356,120  -1.8%
           T9675(optasm) ghc/alloc    444,604,152    428,987,216  -3.5% GOOD
           T9961(normal) ghc/alloc    303,064,592    308,798,800  +1.9%  BAD
           WWRec(normal) ghc/alloc    503,728,832    498,102,272  -1.1%

               geo. mean                                          -1.0%
               minimum                                           -49.4%
               maximum                                            +1.9%

In fact these figures seem to vary between platforms; generally worse
on i386 for some reason.  The Windows numbers vary by 1% espec in
benchmarks where the total allocation is low. But the geom mean stays
solidly negative, which is good.  The "increase/decrease" list below
covers all platforms.

The big win on T13253-spj comes because it has a big nest of join
points, each occurring twice in the next one.  The new occ-anal takes
only one iteration of the simplifier to do the inlining; the old one
took four.  Moreover, we get much smaller code with the new one:

  New: Result size of Tidy Core
    = {terms: 429, types: 84, coercions: 0, joins: 14/14}

  Old: Result size of Tidy Core
    = {terms: 2,437, types: 304, coercions: 0, joins: 10/10}

--------- Runtime perf -----------
No significant changes in nofib results, except a 1% reduction in
compiler allocation.

Metric Decrease:
    CoOpt_Read
    T13253-spj
    T9233
    T9630
    T9675
    T12150
    T21839c
    LargeRecord
    MultiComponentModulesRecomp
    T10421
    T13701
    T10421
    T13701
    T12425

Metric Increase:
    T18140
    T9961
    T18282
    T18698a
    T18698b
    T19695