frameencoder: release row lock while waiting during VBV restarts

This fixes what appears to have been an old deadlock bug that has just recently
become very reproducible
frameencoder: do not use bitmaps for framefilter if not WPP

The non-WPP row loop wants to do frame filter work in between each row, with
a m_filterRowDelay lag. If we use the functions which update the bitmap, it
would allow a worker thread to process a filter row before it was ready.  In
short, the non-WPP path was never intended to work in the presence of a thread
pool. This was causing crashes when --no-wpp --pmode||--pme was used.
asm: avx2 for luma_hpp[64x64, 64x48, 64x32, 64x16]

33137c->22606c , 24826c->17202c , 16726c->11560c , 7830c->5534c
asm: avx2 for Luma_hpp[16x4, 16x8, 16x12, 16x16 , 16x32, 16x64]

619c->458c, 1174c->812c, 1694c->1112c, 2291c->1535c, 4846c->3207c, 9294c->6104c
asm: luma_vpp[16x32, 16x64] in avx2: improve 3875c->2463c, 7499c->4894c
asm: luma_vpp[32x32, 32x64] in avx2: improve 7247c->4909c, 14365c->9774c
asm: luma_vpp[32x16] in avx2: improve 3808c->2491c
asm: luma_vpp[32x24] in avx2: improve 5562c->3899c
asm: luma_vpp[32x8] in avx2: improve 2047c->1472c
asm: luma_vpp[64x32, 64x48, 64x64] in avx2: improve 14150c->9810c, 21132c->14684c, 28663c->19616c
asm: luma_vpp[64x16] in avx2: improve 7245c->4910c
Luma_hpp[32x8 , 32x16 , 32x24 , 32x32 , 32x64] avx2 asm code: improved 2032c->1556c, 4238c->3014c, 6696c->4801c, 8697c->6433c, 16823c->12297c
asm: luma_hpp[8x4] in avx2: improve 357c->261c
Luma_hpp[48x64] avx2 asm code : improved 25053c->17882c
asm: luma_hpp[8x8, 8x16, 8x32] in avx2: improve 623c->523c, 1384c->1083c, 2555c->2058c
slicetype: fix vbv lookahead data collection for all frames within the lookahead window.
rc: tune midframe vbv logic for B frames
rc: use c-style typecasts
rc: limit bit amortization in ABR to longer sequences
rc: adjust qp for B frames from ABR feedback in case of CBR.

limits the bitrate fluctuation for CBR with respect to the target bitrate set.